A clinical trial was performed to evaluate the therapeutic efficacy of osaterone acetate (OSA) in the treatment of benign prostatic hyperplasia (BPH) in dogs. Osaterone acetate (Ypozane, Virbac) was administered orally at a dose of 0.25 mg/kg body weight once a day for seven days to 23 dogs with BPH. During the 28-day trial, the dogs were monitored five times for their clinical signs and prostate volume. The OSA treatment promoted rapid reduction of clinical scores to 73.2% on day 7 and to 5.9% on day 28 (p<0.05). Osaterone acetate induced the complete clinical remission in approximately 83.0% of the dogs on day 28. The prostate volume regressed to 64.3% of the pretreatment volume after two weeks of the treatment (p<0.05) and to 54.7% at the end of the trial (p<0.05). In conclusion, OSA quickly reduced clinical signs and volume of the prostate glands in dogs with BPH.