The objective of this work was to study, through ultrasonographic evaluation, changes in testes and epididymides of clinically healthy, peripubertal and pubertal Santa Inês lambs raised in Brazil. Periodic evaluations of weight, biometric characteristics (scrotal circumference, width and length) and ultrasound examinations of the testes and epididymides of 20 lambs were performed between 84 and 280 days old at intervals of 28 days. Scans were performed in the sagittal, transverse, frontal and oblique planes to evaluate the echotexture of the testicular parenchyma and mediastinum and the tail epididymis as well as the thickness and width of the mediastinum testis. The testicular parenchyma demonstrated a homogeneous echogenicity pattern ranging from low to moderate. The echogenicity of testicular parenchyma increased in direct proportion to animal age, being higher in pubertal lambs when compared to prepubertal at the same age. The mediastinum testis was observed in 100% of the evaluated animals, regardless of the scan plane used, and was classified as diffuse or moderately or highly echogenic. Echogenicity and the thickness of the mediastinum testis increased in direct proportion to animal age. The epididymal tail was presented in hypoechoic relation to the testicular parenchyma. Based on these results, it was concluded that ultrasound is useful tool for selection and morphophysiological evaluation of Santa Inês lambs on peripubertal and pubertal phases, when used in combination with other methods such as semen evaluation.