Acusilaus of Argos was an early Greek mythographer and genealogist active in the late sixth or early fifth century BCE. Ancient sources record his Argive origin, identify his father as Cabas or Scabras, and place him chronologically around the time of the Persian kings Cyrus or Darius I. He is traditionally grouped with early prose writers like Hecataeus of Miletus as a pioneer of historical writing preceding Herodotus.

His major work was the Genealogies or Histories, a prose treatise systematizing mythical traditions from the origins of the cosmos to the heroic age. Now lost, it survives in fragments cited by later authors. These fragments cover theogonic material and heroic genealogies, often presenting variants of myths known from Hesiod and the epic cycle. While some sources mention a separate work On Argos, this is likely part of his larger genealogical compilation.

Acusilaus holds significance as one of the earliest Greek prose authors. His compilation helped standardize and transmit versions of Greek myths, forming a crucial source for later mythographers. His work represents an important step in the development of early Greek historical thought, particularly for the preservation of Argive traditions.