This study aimed to evaluate the effect of immunocastration on the scrotal circumference, as well as in the macroscopic and microscopic testicular features in Nellore bulls bred under a semi-confining system for 91 days. Sixty animals were divided into two groups: 30 intact animals (non-vaccinated) and 30 immunocastrated animals. The immunocastrated animals were treated with two anti-GnRH vaccine doses (BoprivaTM - Zoetis Australia Pty Ltd). The scrotal circumference (SC) was measured on days 0 and 56. Testicular parameters: biometry traits (length, width, and height – cm; volume – cm3 ) and weight (g) was measured on day 91. Three testicles from each group were histologically processed to find the seminiferous tubule diameter and epithelium thickness (µm). Data were analyzed in the Minitab® 19 statistical software. The macroscopic features (SC, and testes weight, volume, length, width, and height) and the microscopic features (seminiferous tubule diameter and epithelium thickness) were compared between the two groups through Student’s t-test and Mann-Whitney test. All the values were lower (p<0.05) in animals immunized against GnRH, except for the right testis width and seminiferous tubule diameter. Results indicate that immunization against GnRH affected testicular development.