The aim of this study was to evaluate the correlation of age and scrotal circumference (SC) establishing testicular growth curve of Nellore bulls. The experiment was carried out in the Jaíta Farm, Macarani-BA, from January of 2004 to January of 2006. There were made 1139 measures of 778 males from 5 to 70 months of age. The animals were grouped into seven classes of age: age 1 (≥ 5 to ≤ 7 months), age 2 (> 7 to ≤ 12 months), age 3 (> 12 to ≤ 18 months), age 4 (> 18 to ≤ 24 months), age 5 (> 24 to ≤ 36 months), age 6 (> 36 to ≤ 48 months) and age 7 (> 48 to ≤ 70 months). The model used to characterize the growth of the SC in function of age was the logistic model, SC= A/ (1+B exp ^-Kt), where SC is the scrotal circumference at t days of age, A is scrotal circumference at maturity, B is the constant integration established by the initial values of SC and t, which adjusts the situation when SC ≠ 0 and/or t ≠ 0, K is maturity constant, which equals the ratio between the maximum rate of growth and SC at maturity. For the logistic function, estimated SC at maturity (A) was 40.0 cm at 70 months of age and inflection point (time of maximum growth) was reached at 11.32 months of age at average SC of 20.0 cm. High and positive correlations between SC and age allow that selection of Nellore males can be indicated to the 12 and 18 months, with SC of approximately 20,15 cm and 25.41 cm respectively.