Examination of the stomach contents of the Japanese mantis shrimp Oratosguilla oratoria showed that this species is a very intensive predator on the Macrura which is a principal component of the benthic megalofaunal community. Thus, the mantis shrimp, by feeding largely on the Macrura, may have a major influence on this community structure in Hakata Bay. The shrimp was also revealed to be an intensive predator on the Pelecypoda despite underestimation of preda-tion intensity, based on the stomach contents, because of its shell-smashing behaviour. Further-more, this study showed that many Macrura were captured during September and November by the mantis shrimp and that female shrimp of reproductive sizes also consume many Pelecypoda, As a prey species, mantis shrimp themselves were found infrequently in the digestive tracts of other predators.