The Chestnut-capped Blackbird, Chrysomus ruficapilus (Vieillot, 1819), is a common bird species in flooded areas of South America. Data on its reproductive parameters have been reported mainly for rice paddies from Uruguay and southern Brazil, where reproductive phenology might have been influenced by the chronology of agricultural activities. Here we provide reproductive data for a population in a natural marshland from São Paulo state, southeastern Brazil. A total of 45 active nests were monitored between December 2017 and April 2018. Clutch size was 2.8 ± 0.44. Incubation and nestling periods were respectively 11.8 ± 0.39, and 12.3 ± 0.75 days, and overall nesting success was 65%. The reproductive season lasted about five months, which is longer than that observed in rice paddies from southern Brazil. This suggests that the reproductive phenology has been underestimated before. Although clutch sizes were bigger in our study population than that from rice paddies from southern Brazil, nest survival was higher in the artificial habitat, suggesting that the Chestnut-capped Blackbird can obtain benefits from nesting in artificial habitats.