Seven specimens of Tylerius spinosissimus (Regan, 1908) were washed up by a typhoon onto a beach at Nakagusuku in Okinawa-jima Island on 17 August 1997. This species has been rarely collected, being known from only a few localities in the tropical Indo-West Pacific. In addition to the seven specimens from Okinawa-jima Island, eight specimens collected off northwestern Borneo in the South China Sea by TV Oshoro-maru in November 1973 were found in the fish collection of the Hokkaido University Museum, Hakodate. Examination of the 15 specimens have revealed that the species is distinguished from other pufferfishes by the following characters: dorsal-fin rays 9–11, anal-fin rays 6–7, pectoral-fin rays 15–17, body somewhat squarish in cross-section, snout short with dorsal surface dropping abruptly anterior to eye, nasal organ a short papilla with two nostrils, eye dorsally adnate only, ventrolateral skin fold absent, body anterior to anal-fin base densely covered by small spinules, dorsal and ventral lateral lines running on lateral surface of body; frontals broad across interorbit, almost completely covering dorsal surface of ethmoid; prefrontal strongly down-curved. A juvenile of Tylerius spinosissimus ca. 10 mm in total length was photographed at 1 m depth in Suruga Bay, on the west coast of the Izu Peninsula, Honshu, Japan, in November 2008. This small specimen was similar in color to adults of T. spinosissimus: the dorsal half of the body being brown with a dark brown blotch just behind the dorsal corner of the eye, the ventral half of body white, and all fins pale.