In order to understand the capture process of trolling line, the fish behavior to an artificial bait of trolling line was observed by a towed underwater video camera. Experimental trolling line consisted of a towing line, a towed underwater video camera, a leader, an artificial bait, and a hook. The experimental trolling line was towed by a small boat at 3 to 6 knots, and the underwater video image were recorded on VCR. A total of 38 hours of the underwater video image were recorded during the experimental period, and the fish behavior to the artificial bait of trolling line could be observed clearly. Fish species that could be identified, were mackerel Scomber spp., frigate mackerel Auxis rochei, amberjack Seriola dumerili, dolphinfish Coryphaena hippurus, yellowtail Seriola quinqueradiata, blowfish Lagocephalus wheeleri, and mullet Mugil cephalus. Fish behavior patterns were classified as follows: appearance into the camera view, approach to the artificial bait, attack on the artificial bait, touching the artificial bait, being hooked, and captured. The total number of appearance into the camera view was 1364, in which the capture was only 23 due to the low attack response frequency to the approaches. From these results, fishing efficiency of the experimental trolling line which is defined as the ratio of the total number of capture to the total number of appearance was calculated to be 0.020 for mackerel, 0.018 for frigate mackerel, and 0.012 for amberjack.