Fresh water crabs are economically important because crabs are used as an alternative source of food by the people (Paithan region) residing near Godavari river and Nathsagar dam. The crabs serve as delicious food and hence it acts as significant human dietary constituents. Heavy metal and their salts containing effluents are directly discharged into the aquatic environment by many industries from Paithan and Aurangabad region. In the present investigation acute toxicity test was carried out to determine the LC50 values (lethal conc.) of mercury chloride by using static bioassay method. The LC50 values for 24, 48, 72 and 96 hrs of exposure were recorded as 2.820, 2.480, 2.257 and 1.980 ppm respectively. In the present study the mercury content in different body parts of fresh crab, B. guerini was studied. The mercury content was found high in all the tissues as compared to control group. The observations in the present study showed marked variation. The highest concentration of mercury encountered in gill.