This study evaluated the effect of paraquat (PQ) and temperature on hematological parameters and nonspecific immune system of fish Colossoma macropomum (Cachama). Juveniles were used for all experiments. Fish were exposed to three temperatures (18, 28, 35°C) and 10mg/L PQ during 21 days (PQ LC(50) 96h was of 48.05mg/L). Hematological (Hb, Ht, VCM, HCM and CHCM and RBC) and immunological parameters (WBC, differential count of white cells, phagocytes, and bacterial killing by phagocytes) were analyzed for 7, 14 and 21 days. Fishes PQ exposed at 18°C decreased Hb, MCH and MCHC; we observed sickle erythrocytes in control group at 18°C, and in PQ-exposed groups at 18 and 35°C. Immunological parameters were not affected by temperature. Neutrophils decreased significantly in all PQ-exposed groups. Bacterial killing by phagocytes decreased in 18 and 35°C PQ-groups; a synergistic interaction was shown between PQ and temperature on WBC and lymphocytes. These results indicate that PQ affected neutrophils counts independently of temperature exposure; the temperature exerted a synergistic effect on PQ toxicity in lymphocyte counts and phagocytic response and besides nonspecific immune response, PQ and temperature affects hematological parameters such as Hb, MCH, MCHC and erythrocytes morphology.