Seth-Peribsen (also known as Ash-Peribsen, Peribsen and Perabsen) is the serekh name of an early Egyptian monarch (pharaoh), who ruled during the Second Dynasty of Egypt (c. 2890 – c. 2686 BC). His chronological position within this dynasty is unknown and it is disputed who ruled both before and after him. The duration of his reign is also unknown.
Peribsen's royal name is a subject of curiosity for Egyptologists because it is connected to the deity Seth rather than Horus, as was traditional for the name of a pharaoh. The debate continues over why Peribsen chose this name. Earlier theories have favoured the idea that Egypt was split in two realms during Peribsen's time or that he was a heretic, who sought to start a new monotheistic religion with Seth as the only worshipped god. However, newer evidence and evaluations tend to show that the Egyptian kingdom was unified, but witnessed a vast and profound reform during the second dynasty. Seal impressions from tombs of this era reveal great changes in the titles held by high officials, pointing to a reduction of their power. Further seal impressions show that several deities were worshipped under Peribsen, refuting the monotheism theory, with other contemporary inscriptions indicating that the Egyptian grammar was perfected during his reign: In particular, the earliest seal impressions with complete sentences date back to Peribsen's reign. Thus, Peribsen's reign was in fact a time of cultural and religious advancement.