Isis Prophetissa is the name given to a pseudonymous author of ancient Greek alchemical texts. The figure is presented as the Egyptian goddess Isis, a common literary device in late antique writings where gods reveal secret knowledge. The actual historical person is unknown. The works are dated to the late antique period, likely between the 2nd and 4th centuries CE, a time when Greek alchemical literature flourished in Roman Egypt.

The author is associated with the Hermetic tradition, which blended Egyptian religious ideas with Greek philosophy and practical craft. The primary surviving work is an alchemical treatise addressed to her son Horus, concerning the making of gold and silver. This text survives only in fragments and citations within later Greek and Byzantine alchemical writings. A second, less distinct work on dyes or the elements is also sometimes attributed to her.

According to modern scholars, Isis Prophetissa represents an important effort to give divine and ancient authority to the craft of alchemy. By attributing technical knowledge to the goddess Isis, these texts aimed to elevate alchemy from a mere craft to a form of revealed temple wisdom. The citations of her work by later alchemists show she was a recognized figure in the tradition. This pseudonymous author illustrates the characteristic blending of Egyptian religion, Hellenistic science, and mystical philosophy in late antique Egypt.