To investigate the CYP17A1 gene mutations in Chinese patients with 17 alpha-hydroxylase/17, 20-lyase deficiency.Clinical data were retrospectively analyzed. The CYP17A1 gene mutations were detected in 5 cases with 17 alpha-hydroxylase/17, 20-lyase deficiency and their relatives. The genomic DNA of the patients was isolated from whole blood. Seven pairs of primers were used to amplify eight exons and exon-intron boundaries of the CYP17A1 gene. The amplified PCR products were purified by agarose gel and then directly sequenced. In order to confirm the DNA sequences of different alleles, some fragments were inserted into pMD 18-T vector and then sequenced. Sequencing results were compared to the established human CYP17A1 sequence.Briefly, we found 2 kinds of compound mutations, of which were: (1) 6436-6438(TAC-->AA), causing amino acid Y329K, 418X; (2) 6531-6532(GC-->A), causing amino acid L361F, 418X. Among the five cases, four were homozygous for 6436-6438(TAC-->AA), whereas one was compound heterozygous for 6436-6438(TAC-->AA)/6531-6532(GC-->A). The clinical characteristics of 5 cases were all completely combined defects of 17 alpha-hydroxylase/17, 20-lyase, and they all carried two alleles of CYP17A1 gene mutations that all shifted the reading frame and resulted in truncated protein which lack of the activity center site of P450C17, of which corresponding with their clinical feature.Nine alleles have the mutation of 6436-6438(TAC-->AA), accounting for 90% of total alleles (9/10). That suggests this kind of mutation may have racial specificity. More study should be done to have better understanding of the function of the truncated P450C17 enzymes.