Abstract: Objective　To report clinical characteristics and genetic results of two sisters suffered from congenital adrenal cortex hyperplasia (17-α-hydroxylase deficiency), and relevant literatures were reviewed. Methods　Clinical manifestation and laboratory examination data of two sister cases of 17-α-hydroxylase deficiency enrolled in Capital Institute of Pediatrics in March 2016 were analyzed. Sanger sequencing and MLPA for CYP17A1 genes were performed and the parents' genes were also verified. Results　The two  patients were four years and 10 years old, both suffered from hypokalemia after infections, and hypergonadotrophin gonad hypofunction. One case was with slightly high blood pressure. Laboratory test results showed potassium fluctuation tendency in 1.9~4.0 mmol/L, 17-OHP and DHEA was decreased. Enhanced CT showed different degree of adrenal gland enlargement. Chromosome examination of the older sister is 46, XY. Both sisters demonstrated heterozygous mutation of CYP17A1 gene.  The molecular genetic analysis suggested a c.985_987delTACinsAA from father and a deletion spanning exons 1-7 of the CYP17A1 gene from mother. Conclusion　17-α-hydroxylase enzyme deficiency can be diagnosed before adolescence. Clinical hypokalemia with unknown reason and high blood pressure may indicate the disease. The diagnosis  can be confirmed with gene sequencing of CYP17A1.