Sosibius of Sparta was a Spartan grammarian and antiquarian of the 2nd century BCE. His scholarly treatises focused on Spartan customs, religious rites, and history, demonstrating deep knowledge of local traditions and earlier poetic sources. No further biographical details survive.

His works are preserved only in fragments cited by later authors. The primary attributions are On the Sacrifices in Lacedaemon, detailing Spartan religious rituals, and On Allegorical Interpretations in Lacedaemon, concerning allegorical explanations. References to works on chronology, the poets Alcman and Epicharmus, and Spartan institutions may represent parts of these core texts.

Sosibius is a significant source for Spartan religion and local history. His fragments were used extensively by later grammarians like Athenaeus, preserving unique cultural details. He represents the Hellenistic antiquarian tradition, providing valuable evidence for modern studies of Spartan society and historiography.