AIM: To detect the germline mutations of hMLH1 and hMSH2based on mRNA sequencing to identify hereditary nonpolyposis colorectal cancer (HNPCC) families.METHODS: Total RNA was extracted from peripheral blood of 14 members from 12 different families fulfilling Amsterdam criteria Ⅱ. mRNA of hMLH1 and hMSH2 was reversed with special primers and heat-resistant reverse transcriptase. cDNA was amplified with expand long template PCR and cDNA sequendng analysis was followed.RESULT: Seven germline mutations were found in 6families (6/12, 50%), in 4 hMLH1 and 3 hMSH2 mutations (4/12, 33.3%); (3/12, 25%). The mutation types involved 4 missense, 1 silent and 1 frame shift mutations as well as 1 mutation in the non-coding area. Four out of the seven mutations have not been reported previously. The 4 hMLH1mutations were distributed in exons 8, 12, 16, and 19. The 3hMSH2 mutations were distributed in exons 1 and 2. Six out of the 7 mutations were pathological, which were distributed in 5 HNPCC families.CONCLUSION: Germline mutations of hMLH1 and hMSH2 can be found based on cDNA sequencing so as to identify HNPCC family, which is highly sensitive and has the advantages of cost and time saving.