Respiration rate is an important parameter to find out physiological and metabolic state of the animal in toxic It can help to evaluate the rate of toxicant entering in the body and affecting the availability of molecular oxygen which is essential for the cell development cellular function and energy metabolism. Oxygen is one of the most important requirements in aerobically respiring aquatic organism. The crab Uca marionis (Desmarest) depends on aerobic mechanism for its energy need. In the present study attempts have been made to investigate and to find out the effect of Malathion pesticide on marine crab U. marionis (Des) at lethal and sublethal concentration both under acute toxicity exposure and chronic toxicity exposure.