The study aims to compare serial changes in prostate-specific antigen (PSA), testosterone, dehydroepiandrosterone (DHEA), and androstenedione in patients treated with either of the antiandrogen agents, bicalutamide or flutamide, using a randomized controlled study. Patients had to meet the following inclusion criteria: (1) presence of histopathologically confirmed prostate cancer, (2) prostate cancer treatment naive, (3) no current treatment with luteinizing hormone-releasing hormone (LH-RH) agonist for sexual interest and physical capacity, (4) clinical stage T1-cT3N0M0, (5) Gleason score ≤ 7, and (6) Cooperative Oncology Group performance status 0-1. Patients were randomly allocated to two groups: flutamide and bicalutamide monotherapy group 1:1. PSA levels were significantly decreased in both groups at 4 weeks. PSA levels were significantly lower in the bicalutamide group compared with the flutamide group at 4 and 8 weeks. Testosterone levels in the bicalutamide group were significantly higher than the baseline levels between 4 and 24 weeks of treatment. Testosterone levels in the flutamide group were significantly increased at 4 and 12 weeks and returned to baseline levels at 16 and 24 weeks. DHEA levels in the bicalutamide group were unchanged from baseline at 4 and 24 weeks. However, DHEA levels in the flutamide group were decreased at 24 weeks. Androstenedione levels increased slightly in both groups, but the increase did not reach statistical significance. PSA, testosterone, and DHEA levels significantly differed between bicalutamide and flutamide monotherapy.