The fish behavior survey in the main-net of a large scale-net was carried out in relation to the catching function of the set-net. at Kishihata set-net in Japan during the period from January 29th to February 22th 1992. The results obtained are summarized as follows; 1. The greatest number of schools observation in the main-net occurred between 17 : 00hrs and 18 : 00hrs. after which the schools suddenly disappeared. This result show that the schools did not stay in the main-net. but immediately moved through into the bag-net or left the main-net. 2. The course of movement of the small schools of sardine in the main-net was in a straight line to the slope-net. However. upon arrived at the slope-net the school turned around. away from the slope-net and went directly towards the playground. 3. The majority of small schools of sardine in the main-net were estimated to move with the mode velocity 25cm/sec. however the maximum velocity were recorded 80cm/sec.