Life history and population size of an endemic Japanese spinous loach, Cobitis takatsuensis, an endangered species, were surveyed in the Hijikawa and Iwamatsugawa river systems, Shikoku Island. The loach was visible on the river bed when water temperatures rose above 13-15°C and throughout this period inhabiting pebble and boulder areas under shallow banks of pools. No significant migration was observed. Hibernation, reproduction and early development were believed to occur deep in the pebble/boulder interstices. Gravid females were observed when water temperatures reached 16-20°C, from May to July, the sex ratio becoming more female-biased during the reproductive season. Adult fish size and minimum female size at maturity were both larger in the Iwamatsugawa River. The mean diameter of ovarian large size eggs which will actually be produced is 1.3 to 1.4mm in the Hijikawa River population, rather smaller than (1.4 to 1.5 mm) in the Iwamatsugawa River, the size and number of eggs of the latter being equivalent to other populations surveyed in the Chugoku district. A mark and recapture exercises indicated each population to comprise less than 400 adults, the high recapture rates, 15-25% of adult fish, suggesting that the populations could easily decrease in size due to overcatching. In addition, limited habitat resources also increase the possibility of the population's accidental extinction. The need for active conservation measures, considering the characteristics and geographical variations in the life history of C. takatsuensis, was also discussed.