The study on the suitable escape gap for modification the collapsible crab trap to be the selective gear by comparing the shape and the position of the gap in the laboratory and comparing the efficiency of bait to find the appropriated one around the coastal area of Sriracha Fisheries Research Station, Chonburi Province, found that the suitable shape and position of the escape gap are square shape and bottom rim side position respectively. Those results may relate to the shape and movement behavior of the crabs. For the most appropriated bait in the laboratory and in the fishing trip experiment are green mussel and raw fish respectively. ...