Abstract: SOD, ATPase, MDH and ME isoenzymes in gill, digestive gland, foot, adductor muscle and mantle of Mytilus edulis were tested and analyzed using polyacrylamide gel electrophoresis (PAGE). The results indicated that four SOD bands were identified in five tissues, and the band with the biggest mobility ratio were found weakly in gill, digestive gland and adductor muscle but not in foot and mantle. Two ATPase bands were found in four tissues except digestive gland. One MDH band was found in five tissues, but the MDH gene expressed strongly in foot and adductor muscle. Two ME bands were examined in foot, adductor muscle and mantle, but the band with smaller mobility ratio was found in gill and digestive gland. Four isozymes showed diverse bands in different tissues, displaying tissue-specificity.