The year 305 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Megellus and Augurinus (or, less frequently, year 449 Ab urbe condita). The denomination 305 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

• Seleucus, former officer of Alexander the Great, considers himself emperor of Persia. He attempts to recover lands taken by Chandragupta that had been a part of Alexander's Empire. Seleucus establishes Seleucia on the Tigris River as his capital.

• Antigonus I Monophthalmus sends his son Demetrius to initiate the Siege of Rhodes, as the city has refused him armed support against Ptolemy.^[1]

• The Romans defeat the Paeligni and take their land, some (those who look well disposed towards Rome) they grant citizenship.^[2]
• The Roman consuls, Marcus Fulvius Curvus Paetinus and Lucius Postumius Megellus, decisively defeat the Samnites in the Battle of Bovianum to end the Second Samnite War.

• Agathocles, unable to come to terms with Deinocrates and the exiles, takes to the field with the remnants of his forces; at the Battle of Thorgium Agathocles defeats the much larger army of the exiles.^[3]
• Deinocrates comes to terms with Agathocles who appoints him a general over a part of his army.^[2]

• Zou Yan, Chinese philosopher (d. 240 BC)
• Arsinoe I, queen of Egypt

• Tiberius Minucius Augurinus