Ptolemais of Cyrene was a Pythagorean philosopher from the Hellenistic period, living sometime between the 3rd century BCE and the 1st century CE. She came from the Greek city of Cyrene in North Africa. Beyond this, no details of her personal life or education are known.

She is credited with writing a treatise titled Pythagorean Principles of Music. The work itself is lost, but fragments of it survive because they were quoted by the later philosopher Porphyry in his commentary on musical theory. In these fragments, Ptolemais acts as an authority, explaining the core principles of Pythagorean harmonic science and distinguishing between different branches of the school's thought.

According to modern scholars, her primary significance is twofold. First, she is one of the very few women known to have contributed to the Pythagorean philosophical tradition. Second, her work provides valuable evidence for the history of ancient music theory. The citations by Porphyry indicate her treatise was a respected, systematic source on the subject. Her existence demonstrates that women could participate in the technical scholarly discourses of the Hellenistic world.