Leeches are medicinally important, and are non-target organisms as far as the pestcontrol operations are concerned. Leeches become the victims of toxicity of various agrochemicals, pollutants etc. in the freshwater ecosystem, due to which their very existence is unnecessarily threatened. Changes in the protein fractions such as sarcoplasmic , contractile and stromal of skin (botryoidal tissue), anterior sucker and posterior sucker of the leech. Hirudo birmanica were studied after treatment with sublethal concentration of malathion (0.01ppm), for 24, 48 and 96 h. The values of the fractions are presented as mg% on the dry weight basis. Amongst the protein fractions in control leeches the contractile proteins were quantitatively more than sarcoplasmic and stromal proteins in all tissues. The protein fractions decreased progressively and significantly (p<0.05) in all tissues of leeches as the period of exposure to sublethal concentration of malathion increased. The results are discussed in the light of physiological response of leech to pesticidal stress.