A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through convergent evolution they have independently evolved external superficial fish-like body plans adapted to their marine environments, including most numerously fish, but also mammals such as cetaceans, and even extinct ancient marine reptiles such as various known species of ichthyosaurs. Most species have only one dorsal fin, but some have two or three.

पृष्ठीय फ़िन कई जलीय प्राणियों की पीठ पर स्थित फ़िन होता है। अधिकांश मछलियों, तिमिगण और (विलुप्त) इक्थोयोसॉर जैसे प्राणियों की पीठ पर पृष्ठीय फ़िन होते है। किसी-किसी प्राणी में दो ऐसे फ़िन भी हो सकते हैं।