Myotonia congenita (MC) is a genetic disease characterized by mutations in the muscle chloride channel gene (CLCN1). To date, approximately 130 different mutations on the CLCN1 gene have been identified. However, most of the studies have focused on Caucasians, and reports on CLCN1 mutations in Chinese population are rare. This study investigated the mutation of CLCN1 in two Chinese families with MC. Direct sequencing of the CLCN1 gene revealed a heterozygous mutation (892G>A, resulting in A298T) in one family and a compound heterozygous mutations (782A>G, resulting in Y261C; 1679T>C, resulting in M560T) in the other family, None of the 100 normal controls had these mutations. Our findings add more to the available information on the CLCN1 mutation spectrum, and provide a valuable reference for studying the mutation types and inheritance pattern of CLCN1 in the Chinese population.