Abstract: Objective To explore the correlation between phenotype and genotype of 5 α-reductase 2 deficiency. Methods The clinical data of five children with 5 α-reductase 2 deficiency were retrospectively analyzed and the relation between their clinical phenotype and genotype were analyzed. Results All of these five children presented small penis and testicular hypoplasia, three of whom had ones similar to the clitoris appearance. The testosterone/dihydrotestosterone (T/DHT) ratio was 10.26-64.99 after human chorionic gonadotropin (hCG) stimulation. Gene detection showed one case had c.680G > A homozygous mutation and the others were compound heterozygous mutations. The mutations were mainly missense mutations, followed by deletion, duplication and nonsense mutations. Conclusion The 5 α-reductase 2 deficiency has different degrees of abnormal genital development. Genetic testing contributed to the diagnosis of this disease.