The diet of Pseudis cardosoi was studied in the Araucaria forest and adjacent grassland ecosystems of southern Brazilian highlands by stomach content analysis of 119 individuals. Frogs were collected in ponds surrounded by different grassland habitats. Besides diet composition, diet diversity and volume were explored. Stomach contents were compared among samples from different habitats and collection times. Male, female, and juvenile diets were also compared. A total of 29 prey categories were identified. The most frequent items in the diet of P. cardosoi were: Diptera (15.4%), Coleoptera (14.2%), Hymenoptera (14.3%), plant remains (12.5%), Hemiptera (5.5%), Odonata naiad (2.9%), Isoptera (2.4%), and Araneae (2.3%). There were no significant differences in diet composition among areas. Significant differences in diet composition among males, females, and juveniles were detected, whereas diet diversity and diet volume did not differ significantly among these groups. Diet diversity was higher during spring and summer (January, February and October) and lower in winter (June and July). Certain items showed frequency peaks along the year, suggesting that the diet of P. cardosoi could vary in response to prey temporal dynamics.