Fishing experiments were carried out in the adjacent sea of Yeongil Bay, the eastern cost of Korea from 2003 to 2004 using the dome-shaped pots with different five mesh sizes (17.1, 24.8, 35.3, 39.8, and 48.3mm) in order to determine the size selectivity of pots for the whelk, Buccinum opisthoplectum. The catch species were composed of Buccinum opisthoplectum (45.4%), Buccinum striatissimum (30.1%), Pandalopsis japonica (9.3%), Chionoecetes opilio (8.9%), and so on. The shell height (l) of Buccinum opisthoplectum caught in the experimental fishing pots was measured. The SELECT (Share Each Length's Catch Total) analysis method was applied with fishing data to obtain master selection curve. The model with the estimated split parameter was found to fit the catch data best. The master selection curve was estimated to be s (R)〓exp (7.833R-10.871)/[1 + exp (7.833R-10.871], where R is the ratio of shell height to mesh size. The relative shell length for 50% retention was 1.388, and the selection range was 0.281. It means that the pots of larger mesh size allow more whelks of small size to escape.