We gathered information on the ecology and fishery of the Japanese mitten crab Eriocheir japonica (de Haan) by sending questionnaires to prefectural fishery stations throughout Japan, in October-November, 1996. E. japonica was found to be widely distributed along the Japanese archipelago except for the south-eastern part of Hokkaido and inland areas such as Nagano Prefecture. The season of downstream migration and reproduction ranged from the autumn to spring, and either autumn or spring was main season in some cases. The fishing season coincides with the migratory and reproductive season. These seasons varied between areas, but no clear trends were observed, e.g., with altitude etc. Upstream migration of young crabs has been observed in several area. In some cases, migrating crabs were ca. 1 cm in carapace width, and were found in the area from the river mouth to the lower region of the river in spring. The occurrence of E. japonica infected by Sacculina gregaria was confirmed only in Toyama Prefecture. In many areas, E. japonica was caught as a food and a commercial fishery occurs, including some cases in which the wholesale prices of the crabs were >2000 yen per kg. In addition, decrease in number or decrease in the size of captured crabs were reported in many areas. Some form of fishery regulation is enforced in more than half of the prefectures where fishing for this crab occurs. Seed production and release of crabs is in progress to protect the resource in some prefectures. However, these actions are still limited to restricted areas within the whole of Japan. The development of action to protect natural resources of E. japonica is clearly required.