This study was carried out to obtain fundamental data on the metabolism of hibernant fish loach, Misgurnus mizolepis. Main focus was on the compositon of muscle components and its changes in fresh - water loach before and after spawning season and before and after hibernation. Distributional changes of carbohydrate, protein and lipid in the muscle tissues were also investigated. Change patterns of miosture and crude protein, and moisture and crude lipid were in inversely proportional, i.e. : moisture amount showed the lowest value after spawnig season, the highest just after hibernation, but crude protein and crude lipid were the highest values after spawning season, and the lowest just after hibernation. Carbohydrate showed the highest value just before hibernation and tended to decrease thereafter. Muco layer of epidermis and muscle cell of hypodermis layer in loach were remarkable in its PAS dyeing degree after sapwning season, and it was presumed to include high percentage of protein or carbohydrate. Dermis layer became thinner before spawning hibernation. Lipid component in female tended to distribute relatively widely in the muscle cell layer before spawning season, but in case of male mainly in muco layer and epidermis layer. It appeared that lipid was spreaded mainly in epidermis and hypodermis tissue after spawning season, while it prevailed in almost all tissues but tended to decrease after hibernation.