Aulacomya adductor muscles with and without prior immersion in polyphosphates were frozen and stored at −30 °C. Expressible moisture of control samples increased after freezing and showed the highest increment at the second week of storage. Actomyosin extractability was not affected by freezing but decreased during frozen storage in both untreated and treated muscles. The reduced viscosity and the Mg2+-ATPase activity of actomyosin in dip-treatment free muscles fell with freezing and frozen storage. Polyphosphates reduced the amount of expressible moisture of the muscles and delayed the decrease in the enzymatic activity of actomyosin. Treatment with polyphosphates did not affect the viscosity of actomyosin. The relative percentages of myosin and paramyosin significantly decreased (p < 0.01) and those of actin significantly increased in actomyosin of both control and treated muscles at 4 weeks of frozen storage. These results would indicate that thin filaments in frozen striated adductor muscle are more stable than thick filaments. Keywords: Striated adductor muscles; myofibrillar proteins; biochemical properties; frozen storage; expressible moisture