We investigated the effects of long-term repeated treatments with a sustainable gonadotropin-releasing hormone (GnRH) antagonist, degarelix acetate, on testicular hormonal secretion, size, ultrasound images, histology and spermatogenesis in goats to assess its efficacy as a chemical castration method. Male Shiba goats (3-6 months of age) were treated subcutaneously with degarelix acetate every 4 weeks for 24 weeks. Plasma testosterone and insulin-like peptide 3 (INSL3) concentrations decreased (P<0.05) within 2 days after the first treatment and remained low until 29 weeks (P<0.05). Scrotal circumference and testicular pixel intensity were lower from 2-6 months and from 1-6 months, respectively, compared to the pretreatment values (P<0.05). The testis and epididymis weights were lower at 24 weeks compared to those in untreated goats (P<0.05). There were no sperm in the seminiferous tubules of testicular tissue sections or in homogenates of the epididymis at 24 weeks. These results suggest that repeated treatment with degarelix acetate is an effective chemical castration method for goats.