Abstract: Objective　To explore the clinical feature, gene mutations and treatment of isolated hypogonadotropic hypogonadism (IHH). Methods　The clinical data from a case of IHH and his families were retrospectively analyzed. The related literatures were reviewed. Results　The propositus was a 7-year-old boy with a small penis and testes, whose younger brother was 5-year-old with a small penis and cryptorchidism. In both boys testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH) levels were low. The GnRH provocation test was not reactive. Their parents denied the consanguineous marriage. Illumina sequencing revealed that both of the brothers had homozygous mutation of GnRHR gene in C.806C>T, and their parents were heterozygous mutations in C.806C>T gene. After confirmation of the diagnosis, human choronic gonadotropin (hCG) treatment was given. The levels of testosterone and dihydrotestosterone were significantly increased after 6 weeks. Conclusion　The combination of clinical phenotype, biochemical analysis, and gene detection is helpful for early diagnosis of IHH.