Polymerichthys is an extinct genus of superficially eel-like aulopiform fish known from the late Oligocene to the middle-late Miocene.

It contains a single described species, P. nagurai from the Middle Miocene of Japan, though several indeterminate specimens are also known from Russia and Italy.

[2] The generic name literally translates as "many meristic fish," in reference to how the fish has numerous meristics units, including how the dorsal fin, which runs down the length of the body starting from behind the head, has somewhere between 300 and 350 rays, and how it has at least 186 vertebrae.

6599, was originally collected by Masayasu Nagura, a suzuri maker, around 1927 from the middle Miocene-aged Tubozawa Formation of Aichi Prefecture.

A jaw of Polymerichthys has also been reported from the middle Miocene of Italy, which appears to be from a taxon highly distinct from the Pacific polymerichthyids based on the number of teeth and the tooth surface texture.