Abstract: To investigate morphological characteristic of muscles in Eriocheir sinensis before and after molt, histology, ultrastructure and main protein contents in walking leg and abdominal muscles of E. sinensis during molt cycle were studied. The results showed that the histology of walking leg muscle at pre- and post-molt was similar with inter-molt. Their ultrastructure had no obvious change in pre-molt stage compared with inter-molt, and it took on visible myofibrillar fissure and sarcomere transverse crack in post-molt, indicating that the muscle was growing while the exoskeleton was hardening. In termers of abdominal muscle, enlarged muscle bounds space in pre-molt stage and enlarged muscle fibers space in post-molt stage were observed. Moreover, there were erode area in myofibril and enlarged inter-myofibril space in pre-molt. The myofibril re-assembled in post-molt and re-covered to the normal form of inter-molt. Myofibrillar protein and soluble protein content in walking leg and abdominal muscle fluctuated and agreed well with their structure. The results indicate that the structural characters of walking leg and abdominal muscles of E. sinensis are closely related to the animal’s molt stage.