Azurin derived from P. aeruginosa MTCC 2453 were reported to be an important modulator in cancer regression which leads it to develop as a therapeutic drugs. Earlier studies reported that azurin derived from P. aeruginosa and other organisms, showed in vitro and in vivo antitumor properties by the induction of apoptosis. The present study was premeditated to evaluate the in vivo therapeutic efficacy of azurin from P. aeruginosa MTCC 2453 in Dalton’s lymphoma (DL) mice model. The acute toxicity assay of azurin showed the 200μg/kg as sublethal doses in normal mice. The acute toxicity like body weight, peripheral blood cell count, lympho-hematological and biochemical parameters remained unaffected till 200μg/kg body weight of azurin. The growth inhibitory properties of azurin against in vivo DL model were vastly significant with its sublethal doses. We found that the DL cells survival rate percentage was 29.69, 64.6 and 88.79% in 50, 100 and 200μg/kg body weight of azurin, respectively. Investigations of the growth inhibitory mechanism in DL cells were exposed by nuclear fragmentation, and the increased accumulation of DL cells in the sub–G₀/G₁ phases in cell cycle analysis are indications of apoptosis. Further, the cause of apoptosis was revealed by Western blot which showed the reduction in the ratio of Bcl-2 and Bax protein expression, the activation of caspases-3 through the release of cytochrome c in DL cells. The survival rate of tumor bearing DL mice treated with azurin analyzed by Kaplan Meir method showed an effective antitumor response as with a dose of 200μg/kg body weight (an 94.19% increase in life span [ILS] %).