The current study was designed to evaluate the comparative effects of three selected chemicals such as emamectin (insecticide), acetochlor (herbicide) and topsin-M (fungicide) on haematology, biochemical profile and histopathology of grass carp (Ctenopharyngdon idella). A total of forty C. Idella was collected from fish farm Hattian Kamra and transported to the Chemistry lab of Government Post Graduate College Haripur in plastic bags containing dissolve oxygen. After acclimatization for a week they were randomly segregated in four groups (E0, E1, E2 and E3) and treated with 5ppb emamectin, acetochlor and topsin-M respectively. After 96hrs of chemical treatment, blood and tissue samples were collected from both control and treated groups for investigation of biochemical and histopathological alterations. Obtained results exhibited significant alteration in haematological parameters i.e. total white blood cells count, MCV, MCH and number of platelets significantly (p<0.05) increased while Red blood cells count, hemoglobin, PCV and MCHC significantly (p<0.05) decreased in the experimental groups E1, E2 and E3 as compared to control group. Significant (p<0.05) changes were observed in biochemical parameters i.e. increase in serum glucose, bilirubin, albumins, blood urea, uric acid, cholesterol, serum calcium, phosphorous, sodium, potassium, serum lipase, CKP, LDH and CK MB, while significant decrease in creatinine, triglycerides, HDL-cholesterol, serum iron, serum amylase, SGPT, alkalinity and Phosphate was observed. The observed Histopathological changes in gills include epithelial lifting, destruction of cartilage core, curling, atrophy, loss and fusion of secondary gill lamellae. In liver tissue, the observed variations were necrosis, pyknosis, lymphocytes infiltration, dissolution of plasma membrane, blood congestion and vacuolation. In tissues of intestine, the alterations found were goblet cell formation, rupturing of villi, necrosis and pyknosis. In heart tissues, histopathological changes included blood congestion, necrosis, pyknosis and vacuolation. It could be concluded that these selected chemicals have a strong tendency to bring variations in haematology, biochemical profile and histopathology of Ctenopharyngdon idella.