To determine the mesh selectivity of a sweeping trammel net for Japanese whiting Sillago japonica, experimental fishing operations using three different inner net mesh lengths (27.5, 31.0 and 33.5 mm) were carried out in Tateyama Bay, Chiba Prefecture, Japan from August to November 1996 and from April to May 1997. The length mode of captured fish increased in proportion to the mesh length from 150–160 mm of the smallest mesh to 190–200 mm total length of the largest mesh. The master curve of selectivity in terms of length ratio to the mesh length (l/m) showed a wide selection range of 50% relative efficiency compared to the mesh selectivity curve of gill net. The curve had a peak at l/m of 6.3 with the selection range from 5.4 to 7.4. This suggested that the trammel net caught a large number of entangled or pocketed fish in comparison to the gilled fish due to the effect of inner net slackness. In terms of body girth ratio to mesh perimeter (G/P), the curve had a peak at G/P of 1.31, which reflected that relative efficiency of capture reached its maximum when the body girth of fish was 1.31 times that of the mesh perimeter.