The year 1503 in science and technology included many events, some of which are listed below.

• July 23 – Unknown at this time, Pluto moves outside Neptune's orbit, remaining there for 233 years.

• May 10 – Christopher Columbus first sights the Cayman Islands, which he names Las Tortugas after the numerous sea turtles there.

• April 21 – Battle of Cerignola: Spanish forces defeat the French, considered the first battle in history won by gunpowder small arms.
• Giuliano da Sangallo constructs the city waIls of Arezzo in Tuscany using the new technology of bastions.^[1]

• December 14 – Nostradamus, French physician and astrologer (died 1566)