Gonadotropin therapy is commonly used to induce virilization and spermatogenesis in male isolated hypogonadotropic hypogonadism (IHH) patients. In clinical practice, 5.6%-15.0% of male IHH patients show poor responses to gonadotropin treatment; therefore, testosterone (T) supplementation can serve as an alternative therapy to normalize serum T levels and promote virilization. However, treatment with exogenous T impairs spermatogenesis and suppresses intratesticular T levels. This retrospective study aimed to determine whether oral testosterone undecanoate (TU) supplementation together with human chorionic gonadotropin (hCG) would negatively affect spermatogenesis in IHH patients compared with hCG alone. One hundred and seven IHH patients were included in our study. Fifty-four patients received intramuscular hCG and oral TU, and 53 patients received intramuscular hCG alone. The median follow-up time was 29 (range: 12-72) months in both groups. Compared with the hCG group, the hCG/TU group required a shorter median time to normalize serum T levels (P < 0.001) and achieve Tanner stage (III and V) of pubic hair and genital development (P < 0.05). However, there were no significant differences in the rate of seminal spermatozoa appearance, sperm concentration, or median time to achieve different sperm concentration thresholds between the groups. In addition, there were no significant differences in side effects, such as acne and gynecomastia, observed in both groups. This study indicates that oral TU supplementation together with hCG does not impair spermatogenesis in treated IHH patients compared with hCG alone, and it shortens the time to normalize serum T levels and promote virilization.