This work aims to characterize the reproductive biology of Oreochromis niloticus, a species of economic and scientific interest with a view to contributing to better management of this fisheries resource. From August 2017 to July 2018, O. niloticus specimens were sampled monthly on the Buyo dam lake. A total of 400 specimens, including and 210 males, were examined. Data analysis indicated a sex ratio in favor of males (1 : 1.10; χ2 = 0.24; pvalue > 0.05). The size at first sexual maturity (LS50) was 14.08 cm for males and 12.88 cm for females. The smallest mature female collected measures 9.5 cm, while the smallest male measures 10 cm. Analysis of the gonado-somatic ratio (GSR) and frequencies of female sexual maturity stages showed that this species reproduces practically all year round, with peaks in July and October. Absolute fecundity varies from 652 to 1,627 oocytes for females between 13.5 and 18 cm in standard length. Relative fecundity is 4 to 9 oocytes per gram of body weight. Mean oocyte diameter just before oviposition is 1.3 ± 0.37 mm.