The problems of seabird bycatch in longline fisheries are thought one of the risks of the seabird conservation. Since population of some bycaught species is vulnerable, to avoid the seabird bycatch effectively, it is crucial to understand how, which species and how many species were bycaught by commercial pelagic longliners. Our study focuses on seabird species for which BPUEs (number of bycatch / 1000 hooks) were high in southern hemisphere. With using Japanese scientific observer data from commercial tuna longline fisheries during 1997 to 2009, average BPUE values of seabirds for each 5°x5° grid cell by each season were drawn. And the factors which affect to number of seabird bycatch: 1) mitigation measure, 2) co-existence of other species, 3) environment, 4) time series: year and month were discussed. Bycaught of albatrosses was the highest in all seabird taxa. BPUE of all seabird species combined was high in south of 25 S, especially off southern African waters and in southeastern Indian Ocean. Number of bycaught albatrosses was affected by number of white-chinned petrels bycaught, sea surface temperature and number of caught fish. The result suggest that bycatch hotspot overlap with where biomass is high.