Apollodorus of Cyzicus was a Greek philosopher from the 5th century BCE. He lived in the city of Cyzicus, a colony on the coast of Asia Minor. According to later historical tradition, he was a follower of Pythagoreanism, a school of thought focused on mathematics, philosophy, and a way of life.

No specific details of his life or education are known. He is credited with a single work, but its title and exact contents have not survived. Given his Pythagorean affiliation and the fragmentary nature of his record, scholars suggest this work may have been a collection of doctrines or sayings from that tradition, but this is not confirmed.

His historical significance appears minimal within mainstream accounts of ancient philosophy. He is not discussed in major modern reference works on the subject. His inclusion in some catalogs of ancient thinkers indicates he was likely a very minor figure. According to modern scholars, his primary importance is as an example of the spread of Pythagorean ideas to the Greek colonies in the eastern Aegean during the Classical period.