A study on the reproductive biology of the Pacific butterfish, Stromateus stellatus, using samples from the coast off Biobío Region (Chile), was carried out. Samples were obtained from fishing vessels during austral spring and summer months. Microscopic analysis shows the presence of oocytes at different developmental stages in the same ovaries, a feature consistent with asynchronous spawning. The frequency of maturity stages shows dominance of mature specimens (90%) in October, previtellogenic in December (33%), and an increase of vitellogenic (73%) and mature (21%) specimens in January. This suggests spawning events in November and February, and a reduced reproductive activity in December. The average size at first maturity was 21.1 cm TL. Partial fecundity varied from 8,340 (TL = 20.6 cm) to 36,210 (TL = 28.1 cm) oocytes. The relationship between partial fecundity and size is represented by Fp = 14.832 TL 2.258 (R² = 0.3043).