Three new species of Parastilomysis, P. paucispina, P. prominula, and P. separata, are described from Japanese waters. Parastilomysis paucispina is different from the other species of the genus by the smaller body size and the uropodal endopod with the inner margin armed with fewer spines, P. prominula by two small protuberances on the mid-dorsal line of the carapace, and P. separata by the arrangement of spines on the lateral margin of the telson. Parastilomysis secunda is revised taxonomically, and a new genus, Hyperstilomysis, is proposed for the accommodation of this species.