Octopus tankahkeei is a new species of cephalopod found recently in the Southern China Sea. It belongs to the class Cephalopoda, Octopoda, Octopodidae and Genus Octopus. Its discovery has attracted much attention from the fisheries industry because it has quickly become a gastronomic favorite of consumers. Because of its popularity, the aquaculture of this species would be of great economical value. The description of the sperm ultrastructure will provide information regarding the fertilization mechanism of this organism and yield an understanding of the optimal method to culture this species. In this report, the ultrastructure of the spermatozoon of Octopus tankahkeei was investigated using electron microscopy. The mature spermatozoon consists of three parts: head, neck and tail. The head contains an acrosome and the nucleus. The spiral and cone-shaped acrosome has many equidistant striations on its surface. The thin cylinder-shaped nucleus has a deep concavity at the post fossa. The neck contains mainly the basal body. The basal body, which is located in the post fossa demonstrates a typical 9 2 arrangement of the axoneme. The axoneme is surrounded by 9 bundles of peri-condensed fiber that parallel the axoneme, forming the “9 9 2” arrangement. The tail is composed of middle piece, principal piece and end piece. The “9 9 2” arrangement of the middle piece is enwrapped with a mitochondrial mantle and a fibrous sheath outside. The principal piece begins at the site where the mitochondrial mantle disappears, but is still enwrapped with a fibrous sheath outside. The end piece begins at the site where the fibrous sheath disappears, but contains 9 bundles of peri-condensed fibers that taper backward. Granular material appears on the exterior of every peri-condensed fiber and diminishes gradually until it completely disappears along with the peri-condensed fiber. The end piece terminates with typical 9 2 arrangement.