We described a new species of cockroach, Periplaneta gajajimana sp. nov., which was collected in Gajajima, Kagoshima-gun Toshimamura, Kagoshima Prefecture, Japan, on November 2012. The new species is characterized by its reddish brown to blackish brown body, smooth surface pronotum, well developed compound eyes, dark brown head apex, dark reddish brown front face and small white ocelli connected to the antennal sockets. In male, the tegmen tip reach the abdomen end or are slightly shorter, while in the female, it does not reach the abdominal end and exposes the abdomen beyond the 7th abdominal plate. We confirmed the validity of this new species by breeding the specimens in our laboratory to demonstrate that the features of the progeny were maintained for several generations. For comparison and easy identification of this new species, the key to species identification of the genus Periplaneta that had been reported in Japan to date are also presented.