AIM: To detect the germline mutations of hMLH1 and hMSH2 based on mRNA sequencing to identify hereditary non polyposis 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 sequencing analysis was followed. RESULT: Seven germline mutations were found in 6 families (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 repotted previously. The 4 hMLH1 mutations were distributed in exons 8,12,16, and 19. The 3 hMSH2 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. AIM: To detect the germline mutations of hMLH1 and hMSH2 based on mRNA sequencing to identify hereditary non polyposis 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 were used with primers and heat-resistant reverse transcriptase. RESULT: Seven germline mutations were found in 6 families (6/12, 50%), in 4 mutation of 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 frame mutation in the non-coding area. Four out of the seven mutations have not been repotted previously. The 4 hMLH1 mutations were distributed in exons 8, 12, 16, and 19. The 3 hMSH2 mutations were distributed in exons 1 and 2. Six out of the 7 mutations were pathological, which were distributed in 5 HNPC C 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.