Muscle fibers and their molecular composition are the important base for evaluation on fish meat quality. To fully understand the characterization of fasttwitch and slowtwitch muscles of mandarin fish Siniperca chuatsi, histological characters of two different skeletal muscles (fasttwitch and slowtwitch muscles) were analyzed by paraffin sections, and these two muscle fibres had different shapes and diameters. Protein compositions of fast muscle and slow muscle were compared according to the number of protein bands and their mobility separated by polyacrylamide gel electrophoresis (SDS-PAGE), and some specific bands existed in 50-60 ku and 10-15 ku. The subfragment1(S1) cDNA of the fast and slow muscle moysin heavy chain were cloned and sequenced by PCR method, the S1 sequences of fast and slow muscle were 2 523 bp and 2 520 bp, which encoded 841and 840 amino acids, respective. They shared 87.6% identities in amino acid sequence, of which loop-1 and loop-2 regions were highly variable. These results showed that fast muscle and slow muscle had significant differences at histological, protein composition and molecular levels, which suggested their different motion functions.