The aim of this investigation was to evaluate the ameliorative role of vitamin-C against the toxicity of dimethoate on Clarias batrachus. Total- 40 mature fishes were divided into four groups of ten each. Group first served as control and received normal diet i.e. Tokyo fish food (2g/fish/day), group second fed with normal diet and exposed with the dimethoate (0.45 ppm), group third received of dimethoate (0.45 ppm) and supplemented with vitamin-C (50 ppm),while, group four received vitamin-C (50 ppm) only for 30 and 60 days. The body weight and hematological parameters i.e. Red Blood Cell, White Blood Cell and Haemoglobin percentage were analyzed after 30 and 60 days. The exposure of dimethoate significantly decreased the body weight after 30 and 60 days. While, dimethoate elevated significantly the White Blood Cell counts but it lowered the number of Red Blood Cell counts and Haemoglobin percentage significantly after 30 and 60 days as compared to control groups. Apart from this, the co-administration of vitamin-C along with dimethoate ameliorated the toxicological effects of dimethoate after different duration in cat fish Clarias batrachus. All these results suggest that dimethoate modulates the hematological parameters in fresh water fish Clarias batrachus, while vitamin-C can ameliorated against oxidative stress caused by the dimethoate toxicity.