The responses of red tile fish, Branchiostegus Japonicus to a longline gear were examined in an experimental tank using two video cameras, in order to know hooking mechanism and improve longline hook. In attraction stage, the fish swim to upstream direction slowly just above the bottom toward the baited hook. The majority of the fish then biting the bait incompletely, after the biting, the fish made a backward swimming with low intense, and the bait was usually spitting out when snood was stretched. In most case, hooking took place at the moment the fish made jerk or rush after the bait wallowed. The behaviour sequence closely related to hooking are chewing and jerking or chewing and rushing. According to the field experiments, the tested hooks of long shank show very low catching efficiency compared to the traditional hook with short shank, and the hooked position of the traditional hooks were oesophagus or stomach but the tested hooks were mouth in the most cases. For catching efficiency, desirable hook shape were inferenced inner-curved point and short shank because its ease to swallow. The shape and demensions of a porposed hook were determined in consideration of mechanized gear handling and hooking performance.