Aristides the Music Theorist was a late antique Greek author active in the late third or early fourth century CE. The epithet "Quintilianus" suggests a possible connection to the Roman rhetorician Quintilian, though this remains unconfirmed. He is known only for his work on music theory and is distinguished from the second-century orator Aelius Aristides.

His sole surviving work is the comprehensive treatise On Music, which exists complete in three books. This treatise is a vital source for late Roman harmonic theory, musical ethics, and the pedagogical and cosmological role of music. It synthesizes Pythagorean and Aristoxenian harmonics with Platonic and Neoplatonic philosophy, systematically detailing scales, intervals, and rhythms while emphasizing music's moral and psychological effects. On Music is a key document for understanding the philosophical foundations of ancient music theory.