Abstract: Malnutrition involving protein deficiency, which commonly occurs in cancer patient receiving anticancer drugs, is considered to be a risk factor for the development of toxicity. Therefore, current study is directed to investigate the possible effects of protein deficient diet on the therapeutic activity and toxicity of paclitaxel in mice bearing Ehrlich ascites carcinoma cells. Administration of a single dose of Paclitaxel (10 mg kg -1, i.p.) decreased the tumor volume significantly in normally-fed animal (23%), while animals on deficient protein diet, the tumor volume decreased non significantly amounting to 13%. The long term survivors were increased by 58 % in normally fed tumor bearing animals compared to only 20 % in protein malnourished bearing animals after treatment with the same dose of paclitaxel. Moreover, 24 h after paclitaxel administration the serum level of lactic dehydrogenase activity significantly increased by 42% in protein deficient animals in compare to 12% in normally-fed ones. The activity of lactic dehydrogenase return to normal level 72 h after paclitaxel administration in normally fed-animals. In contrast, animals on protein deficient diet the activity still high (40%). In conclusion, paclitaxel administration exerts less therapeutic activity and more toxic effects in protein malnourished animals compared with normally-fed animals.