In order to estimate catch efficiency of a small seine (1.0 by 2.3 m, 2 mm mesh aperture) for larval and juvenile Japanese sea bass Lateolabrax japonicus, results from experimental hauls of the small seine were compared with those from a large seines (1.0 by 16 m, 2.5 mm mesh aperture) in the Ohta Diversion Channel on March 21 and April 7, 2008. A total of 1,502 Japanese sea bass, ranging between 14.5 and 24.0 mm in standard length were collected. Data of fish <15.9 mm was excluded from the analysis since extrusion of these fish through the mesh of the large seine was possible. Comparison of the Japanese sea bass abundance at lengths between the small and large seines revealed that the catch efficiency of the small seine for Japanese sea bass <18.0 mm was approximately 100%. The catch efficiency decreased with the increase in fish body length between 18.0 and 22.9 mm. A linear model was fitted to the relationship between the catch efficiency (C, %) and body length (L, mm): C=－17.2*L+388.8 (n=11, r2=0.77, p=0.0004). Catch efficiency was not estimated for Japanese sea bass ＞ 23 mm since their abundance was quite low in the surveyed area probably due to migration to downriver or sea areas, which are considered as habitats for the following life stages.