Biparental care is the dominant (81 %) form of parental care in birds. The degree of sexual selection and the resulting mating system and parental care type have been determined, in many cases, by inference from external characters of sexual dimorphism. The lack of information and the biological attributes of the tyrant flycatchers (e.g., low sexual dimorphism) make it difficult to determinate the parental care roles in most species. Tyrant flycatchers comprise a diverse bird family, but information on the reproductive behavior of many Tyrannid species is lacking. Our aim was to describe external sexual characters (morphology and coloration) and determine the parental care behavior at the nest in the Warbling Doradito (Pseudocolopteryx flaviventris), especially considering the potential role of sexual differences in relation to parental roles at nest. We studied the parental care behavior during two breeding seasons. Parents were captured to take morphological measurements and a blood sample for molecular sex determination. We found that parental care in the Warbling Doradito was biparental biased toward females, where the incubation was performed exclusively by females and the 74 % of activities of nestling brooding and feeding was performed by females. We also found sexual differences, slight in size and plumage, but more conspicuous in bill color. Despite the relatively slight sexual dichromatism of the Warbling Doradito, the parental care behavior in the nest was biased towards females, and the assistance of males to nestlings was highly variable and was not correlated with either clutch size or increasing nestling mass. Therefore, the evidence presented here suggest that Pseudocolopteryx genus may have an unusual social system, otherwise uncommon in tyrannids.