On an intertidal sand flat in west Kyushu, Japan, populations of the ghost shrimp Callianassa japonica ORTMANN and the snake eel Pisodonophis cancrivorus (RICHARDSON) were found to inhabit the upper and lower tidal zones, respectively, in August, 1979. Ghost shrimp distribution later expanded greatly, and in September, 1987, when almost the entire sand flat was densely populated by ghost shrimps, the density of snake eels was found to have increased significantly from that recorded in 1979. This may have resulted from immigration of adult snake eels onto the sand flat from elsewhere. Possible beneficial effects of ghost shrimps with regard to snake eels are : 1) an increase in softness and underground water content of the sediment owing to the turnover of sediment by and the presence of burrows of ghost shrimps. Such bioturbation is more favorable for snake eels' penetration of and resting in sediment ; and 2) ghost shrimps are a preferred food of snake eels. Both 1979 and 1987 studies recorded ghost shrimps as prey of snake eels, larger-sized shrimps being almost the exclusive prey item in 1987. The predation impact of the snake eel population on the ghost shrimp population is estimated to be trivial.