Changes during storage at 0°C in the frequency of specimens in rigor, breaking strength, rate of muscle fiber contraction, and concentrations of ATP and its related compounds were examined in the adductor muscle of the scallop Patinopecten yessoensis that was washed by different methods. All scallops were in rigor on day 2 after washing in distilled water, and on day 5 without washing or after washing in artificial sea water. The scallop was in rigor when the muscle fiber contracted over 25%. Breaking strength, ATP concentration and pH decreased more rapidly during storage in samples washed in distilled water than those not washed or washed in artifial sea water, while K value was increased more remarkably by the former treatment. These results suggest that washing treatment of scallop adductor muscle with water even for 2 short time is unsuitable, and that washing in sea water is more desirable.