Sub-inspector (SI), or sub-inspector of police or police sub-inspector (PSI), is a rank used extensively in South Asia: in the police forces of Bangladesh, Pakistan, India, and Sri Lanka, which are primarily based on the British model. It was formerly used in most British colonial police forces and in certain British police forces as well. The rank usually was in charge of a police substation or assisted an inspector.

The rank of sub-inspector was introduced into the Metropolitan Police in the late 19th century. It did not last long, being effectively replaced by station sergeant in 1890. Officers who already held the rank retained it, and were promoted to inspector as soon as a vacancy arose.

In the Metropolitan Police, a rank wearing one star was formerly officially known as a "station inspector" to distinguish it from the more senior rank of sub-divisional inspector that was abolished in 1949.

The Royal Canadian Mounted Police rank of sub-inspector was introduced in 1942 with the insignia of one star, similar to an army second lieutenant. This was changed in 1960 to three stars, similar to an army captain. It was disestablished in the reorganization of 1990, which eliminated the RCMP's subaltern ranks.^[1]

The rank of sub-inspector was eliminated in 1970.^[2]

The rank of sub inspector was replaced after the Rhodesian Unilateral Declaration of Independence with three grades of; patrol officer, senior patrol officer and section officer with one, two, and three gold coloured bars respectively.^[3]

Sub-Inspector of Police
Service branch	Civil (General Executive), Armed Reserve Police, Technical
Abbreviation	SI, PSI
Rank group	Lower Subordinate Officers
Next higher rank	Inspector of Police
Next lower rank	Assistant sub-inspector of police
Equivalent ranks	Sergeant

A sub-inspector (SI) is generally in command of few police personnel but this is the junior in-charge of Police Station Department (with head constables, the equivalent of corporals, commanding police outposts). It is the lowest rank of officer who, under Indian Police rules and regulations, can file a charge sheet in court, and is usually the first investigating officer. Officers subordinate to them cannot file charge sheets, but can only investigate cases on their behalf. They can be station house officers in some states, like Kerala.

A sub-inspector ranks above an assistant sub-inspector of police (ASI) and below an inspector of police. Most sub-inspectors are directly recruited into the police and have better educational qualifications than lower-ranking police officers.

Specialised units such as the Central Armed Police Forces, State Armed Reserve Police and Armed Battalions use the same rank, but generally these officers do not have any investigative powers. There are also specialist non-investigative officers in the police forces, such as sub-inspector (band), sub-inspector (motor transport) and sub-inspector (telecommunication).

The rank insignia for a sub-inspector is two (five point) stars, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a subedar in the Indian Army. An assistant sub-inspector has one (five point) star, and a red and blue striped ribbon at the outer end of the shoulder straps. This is similar to the insignia of a naib subedar in the Indian Army. The rank insignia for principal sub-inspector and additional sub-inspector are the same.

For the post of sub-inspector and assistant sub inspector, a Staff Selection Commission (SSC) recruits eligible candidates on national level in various Central Armed Police Forces like BSF, CRPF, ITBP, SSB, CISF, and other Central Police Organisations, such as CBI, RPF. Sub Inspector of Central Armed Police Forces and State police Forces have same scale and pay level. But subedar and Junior Junior Warrant officer of Indian Armed Forces i.e. Indian Army, Indian Navy and Indian Airforce have other pay level and payment privilege which is better than Central Armed Police Forces or State police forces.

In 2024 Manvi Madhu Kashyap became India's first openly transgender sub-inspector.^[4][5]

In the Royal Malaysia Police (PDRM), the rank of sub-inspector is the senior-most of non-commissioned officers. They are also the lowest ranking police officers to wear their rank insignia on epaulettes on both shoulders. A sub-inspector of the PDRM ranks immediately above a sergeant major (SM) and below a probationary inspector (P/Insp).

In the Nepal Police, the rank of sub inspector is generally the next senior rank from assistant sub inspector (ASI) and is less senior than an inspector. Members holding the rank usually wear an epaulette featuring two silver stars, the same rank badge as a sub inspector in the Armed Police Force.

In the Sri Lanka Police Service, sub-inspector of police (SI) ranks above that of police sergeant major (PSM) and below an inspector (IP). Generally an SI is the officer in charge (OIC) of a small police station, a detachment of police personal or deputy OIC of a larger police station in a metropolitan area.

Most sub-inspectors are directly recruited into the police service as probationary sub-inspectors for one year's training. The basic educational entry requirement is that an applicant has passed the G.C.E Advance Level Examination. Annually, a number of other officers come up through the ranks and are promoted to rank of SI. The rank insignia for a sub-inspector is one star.

In the Romanian Police, subinspector is the lowest commissioned rank, below inspector, and corresponds to the former rank of police second lieutenant (see Romanian Police ranks).

• Royal Hong Kong Police
• Palestine Police (before 1948)^[3]
• Mossos d'Esquadra