In the present study, the cat fish Heteropneustes fossilis (Bloch) was treated with the sub-lethal doses of the organophosphorus pesticide dichlorvos and malathion for 10 days, 20 days and 30 days to observe comparative changes in excretory function among the fishes. LC50 value of Dichlorvos and Malathion were calculated by probit analysis (Finney, 1964) and sub-lethal concentration of 2.5 ppm and 5 ppm Dichlorvos and 0.1 ppm and 0.2 ppm Malathion were prepared by using standard technique (APHA, 1985). In this study, acclimatized fishes were divided into a control group (Group 1) which is being freed from the treatment of the pesticides and Experimental group 2 and 3 were treated with sub lethal doses of the pesticides dichlorvos and malathion respectively. A significant dose and duration dependent alteration was observed in the level of serum ammonia, serum urea, serum creatinine, and GLDH activity in the liver tissue among the experimental group of fishes exposed to dichlorvos and malathion. It was observed that the changes were significantly higher among the fishes exposed to dichlorvos compared to malathion treated fishes.