This document introduces the recent activities and outcome of Japanese scientific observers onboard the commercial krill fishing vessel from 2003/04 to 2007/08 fishing seasons. Main fishing grounds of the Japanese fishery were the Subareas 48.1, 48.2, and 48.3. Recent observation effort was concentrated to the Subarea 48.3. The observer coverage was 32.2 – 51.4 %, and exceeded 50 % in 2007/08 season. The Japanese scientific observers are trained through an educational program on fishery, krill and bycatch species in order to ensure their skill in data and sample collection. Resultant data and samples are analyzed through a cooperative scientific network on Antarctic ecosystem. Biological analysis of the incidentally caught species yielded guidelines for sampling and species identification of larval and juvenile finfish, which was reflected to the CCAMLR observer protocol. Pathological analysis of the krill samples revealed the occurrence of black-spot disease in Antarctic krill and its relation to bacterial infection. Japanese scientific observer activities have thus made considerable contribution to fishery management and marine science. The Japanese government will ensure a certain level of observer coverage to provide information for the management of fishery, krill resources and Antarctic ecosystem.