Skipjack tuna () is the largest component of the tuna fishery throughout the western and central Pacific Ocean (WCPO) and it is the main targeted species in purse-seine efforts in the region. Purse-seine fleets usually operate in equatorial waters, from 10°N to 10°S, and the purse-seine fishery is classified into two set types, termed associated and unassociated sets. These set types have different spatial distribution characters. We used point-pattern analysis (PPA) to explore the relationship between the set types. PPA is an important area of spatial analysis and it is increasingly being applied to fishery-related studies. PPA can identify patterns indicative of an underlying process, and it can identify inter-point interactions, which are of primary interest in ecological studies. Using 2015 logbook data from 23 vessels belonging to Chinese fishery companies, we applied the point-pattern methods of the pair correlation function ) and mark correlation function ), to study the spatial distribution and competing relationship of two types of skipjack schools: free (unassociated) schools and associated schools. Key results are as follows: (1) The spatial distributions of both the unassociated and associated schools of purse-seine skipjack were heterogeneous. Both showed an aggregated distribution over almost all the scales in the study windows, although the spatial patterns of the unassociated school were random at the range of 1.9-2.3 degrees scales. From this we could conclude that at two different lifespans the skipjack in WCPO both are attracted to each other and prefer to aggregate, and hence random characters were much weaker than that of the aggregated. The spatial distribution likely showed aggregated characters because skipjack prefer to inhabit the eastern part of warmer and less-salty water, where the surface water masses and salinity fronts permanently converge, thereby supporting plentiful food organisms for skipjack. The random characters were likely attributable to the patchy and random distribution of the food organisms, which could be unsustainable for skipjack; yet, in WCPO, the highly migratory skipjack are able to follow the movements of the food organisms. (2) There was a negative correlation between the unassociated and associated skipjack schools at the range of 0-0.35 degrees scales, indicating that the two types of schools are in competition within smaller scales. With increases in scale, a competitive relationship, as caused by limited food availability, possibly faded and an independent relationship appeared. We conclude that there is probably no prey relationship between the two types of skipjack schools because there were no attraction relationships at any scale. (3) The CPUE marked point patterns showed a positive correlation with the spatial distribution of associated schools at the scale of more than 0.8 degrees, thus revealing windows of ‘hot spots' and ‘cold spots'; meanwhile, only random relationships were identified at the other scales. The CPUE marked point patterns showed a random relationship with the spatial distribution of unassociated schools at any scale.