Growth of immature Lates japonicus in eelgrass (Zostera japonica) beds of the Tomouchi River located at around 4.3 km upstream from the river mouth of the Gokase River, Kyushu Island, Japan was studied by the mark and recapture method and scale reading from September 1998 to March 2004. Newly occurring 0-year-old L. japonicus specimens of 13.9–78.0 mm SL (standard length) in Z. japonica beds of the Tomouchi River in August or September reached sizes ranging 58.8–125.7 mm SL by April and 203.4–232.8 mm SL between October and November of the following year. Monthly changes in specific growth rates of individuals demonstrated that rapid growth months of immature fish were limited to the period of high water temperature (22–28℃) from June to October. Also, it was supposed that the large-sized fish of the 0-year-old fish migrated away from Z. japonica beds after December, however a few fish remained in Z. japonica beds until the following November.