Congenital adrenal hyperplasia (CAH) is an inherited autosomal recessive disease which results in steroid hormone metabolism disorders. Steroid 11beta-hydroxylase deficiency due to mutations in the CYP11B1 gene is the second most common cause of CAH while CYP11 deflection is the first one. In this study, the authors investigated in blood sample of a male patient suffering from flaccid paralysis of limbs and skin pigmentations. The biochemical and clinical tests revealed symptoms of CAH. The patient's entire CYP11B1 gene was amplified and PCR products were directly sequenced to identify mutations. Two missense mutations in the CYP11B1 gene were detected (p.R43Q, CGG -- CAG and p.A386V. GCG -- GTG) in heterozygous forms. Protein expression of two mutations (p.R43Q and p.A386V) in the animal cell line COS-1 showed 11beta-hydroxylase activity was impaired 45 percent 7.5 percent by p.R43Q mutation meanwhile this activity kept unchanged in terms of p.A386V impact. This result represented the correlation between genotype and phenotype of CAH patient. Finally, the combination of the results of molecular genetic and clinical and biochemical rcsearchs can make it easier for doctors to bring out correct treatment ways and give useful advices to patients as well as his family.