Diel variation of short-term in species composition and abundance of fish in a Zostera marina bed were investigated with 3-h intervals during 24 period in spring tide (14∼15 day) and neap tide (6∼7 day) in April, 2006. A total of 1,084 fish belonging to 22 species were collected from an eelgrass bed at spring tide, whereas 782 fish belonging to 18 species were at neap tide. The common fish species were Acentrogobius pflaumii, Pholis fangi, and Hexagrammos otakii both spring and neap tide. Pseudoblennius percoides, P. cottoides, and Sebastes inermis were also dominant fish species at spring tide, however, Takifugu niphobles, Conger myriaster, and Platycephalus indicus were abundant at neap tide. These were primarily small fish species or early juveniles of larger fish species. Diel variation of short-term in both species composition and abundance were large: most of fish species were higher abundances at nighttime. The peak numbers and biomass of fishes occurred at 20:00 and 23:00 in high tide, whilst those of fishes were the lowest at 11:00 and 14:00 in low tide both spring and neap tide. Diel variation of short-term in the abundance of fishes were influenced by tidal range and cycle, and day-night differences of food availability indirectly.