From the four tuna purse seiners operating in the western equatorial Pacific waters 370 tuna schools were sampled on attribute of the school, fishing operation of purse seine sit and catch. The data were tabulated and subjected to the statistical tests of independency on the associated object and availability of the school, and catch per set of purse seine fishery as well. The resultant inferences are as follows. 1. Most frequent attributes of the tuna schools found on the surface are associated with sea birds, bait fishes and the flotsams. 2. In fishing operations of purse seine sets on the flotsam-associated schools, the settings were more frequently performed at dawn than in day-time. In fishing operations on the sea-birds-associated schools, the siftings were more frequent in day-time than at dawn. 3. From the flotsam-associated schools the successful sets were significantly more frequent. 4. In the fishing operations of purse seine sets, some of the flotsam-associated schools were subjected to the supplementary sets in success to the initial sets until the schools were consummated. 5. The fish-attracting effect of the flotsam is correlated with structure of the flotsam, but not with length of the flotsam. The flotsams, which tend to attract large tuna schools are the complicated-structure flotsams, i, e. driftwoods with roots or branches or with both of them, otherwise a bunch of uprooted bamboo shrubs, while a log without roots and branches tend to be an attractant inferior to the flotsam of complicated structure.