The determination of hematological values is used to obtain knowledge about the health conditions of animal species. The big-headed Amazon River turtles, (Peltocephalus dumerilianus)are considered one of the least known testudine species concerning their biology and health status. Herein, we determined the hematological and plasma biochemical parameters of 17 (eight males and nine females) adult P. dumerilianusto provide reference interval values for clinically healthy individuals. We collected the blood samples by puncturing the femoral vein using long heparinized hypodermic syringes. Sexual dimorphism for individuals was determined by external observation of the shape of the plastron. The average values obtained for the ten hematological and biochemical parameters analyzed were red blood cell count = 0.32 million µL-1; hematocrit = 20.6 %; hemoglobin = 8.5 g dL-1; mean corpuscular volume = 681.6 fL; mean corpuscular hemoglobin = 267.8 pg; mean corpuscular hemoglobin concentration = 41.9 g dL-1; glucose = 80.6 mg dL-1, total protein = 4.1 g dL-1, triglycerides = 388.9 mg dL-1, and total cholesterol = 79.3 mg dL-1. Despite the sexual dimorphism evidenced for the species, there was no significant statistical difference between males and females for both hematological and biochemical parameters analyzed herein. Based on these results, the population is considered healthy, with parameter values coinciding with previously reported reference ranges for testudines species in the region. The results obtained in this study can be used for assessing the health status of other Amazonian turtle populations, especially in actions aimed at cultivation strategies, management, and species conservation.