To evaluate the impact of parathion on aquatic organisms, a freshwater bagrid catfish (Pseudobagrus fulvidraco) was exposed to sublethal concentrations $(63,;95,;190;and;380;{mu}g/L)$ of parathion, organophosphorus pesticide for 30 days. Glucose level in the serum of the bagrid catfish was significantly increased than that of control groups in the $190;{mu}g/L$ concentration at 30 days and in the $380;{mu}g/L$ concentration after 10 days. Bilirubin level was significantly increased in the $190;{mu}g/L$ concentration at the end of the experiment. After 10 days, a significant differences of lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) activity increased in the ${geq}190;{mu}g/L$ and $380;{mu}g/L$ groups. Though cholesterol concentration was stable, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in serum were significantly reduced in the $190;{mu}g/L$ at 10 days and in the $380;{mu}g/L$ concentration at the end of the experiment. In conclusion, if P. fulvidraco was chronically exposed to ${geq}190;{mu}g/L$ concentration of parathion, the hematological changes may be induced due to the stress response.