Objective. Determine the age and body weight at the onset of puberty in Criollo Obispo lambs from a sheep herd. Materials and methods. The present study was carried out ex situ (18⁰ 15’ 52’’ LN). 10 lambs born during the spring were used, which were detected at 3 m of age. The detachment of the urethral process was verified at the age of 5.0 to 5.5 months of age. A semen sample was taken every two weeks with the help of an electro-ejaculator. Sperm concentration was evaluated with a digital photometer, while light microscopy was used for progressive motility and sperm morphology. The Kaplan-Meier procedure was used to estimate the risk or survival time function.to determine the days of onset of puberty. A male is considered to have entered puberty when the ejaculate registers at least 150 million sperm per mL, with a minimum of 50% abnormal cells and a motility greater than 30%. Results. It was observed that the average age of onset of puberty was 211.4±25.09 d, with a body weight of 19.3±1.27 kg. Conclusions. Criollo Obispo lambs begin puberty at 7 m of age and with a body weight of 19.3±1.27 kg.