Nahr as-Sinn (Arabic: نهر السن) is a river in Syria which marks the borders between Tartus Governorate and Latakia Governorate.

In ancient times, the river was called "Siyannu" which marked the southern borders of Ugarit.

[1] Nahr as-Sinn rises in a plain area in Tartus Governorate and runs to the west to finally flow into the Mediterranean Sea south of Arab al-Mulk.

Despite its length which is only 6 kilometres (3.7 mi), it is considered the richest river in Syria.

This article related to a river in Syria is a stub.