Increase in population have led to the rapid enhancement in use of chemicals for industrial as well as house hold purposes. These chemicals affect the life of individuals and also the environment. The mercury compounds have shown ecotoxic potential. Mercuric chloride enters into aquatic as well as terrestrial ecosystem through industries. Mercuric chloride through distribution goes to the composition of the blood and affect the metabolism.The LD50 of mercuric chloride in the present investigation has been observed to be 9.26 mg/kg b.w. on the basis of probit analysis and the toxicity has been observed to be dose dependent.The effect of mercuric chloride on certain haematological parameters in albino rat, Rattus norvegicus have been observed after acute (1 day) and sub-acute (7, 14 and 21 days).