The aim of this study was to evaluate the reproductive strategy of Aequidens tetramerus in small streams of the Machado river basin, southwestern Amazon. We collected samples in two streams using seine and dip nets along a 50-m stretch of the stream. We collected 86 fishes, 19 males and 67 females (sex-ratio, 3.52 female:1male). Their body size varied from 1.5 to 11.5 cm. The size at first reproduction was 1.8 cm for females and 2.0 cm for males. The reproductive season of the species occurred in the dry period.