Introduction: Natural phytochemicals are considered safe to use as therapeutic agents. There is a growing trend toward exploring anticancer effects of crude algal extracts or their active ingredients. Euglena tuba, a microalga, contains excellent antioxidant potential. However, the anticancer property of E. tuba has not been explored. This study investigates the chemical profiling as well as antitumor property of methanolic extract of E. tuba (ETME) against Dalton’s lymphoma (DL) cells. Materials and Methods: E. tuba, procured from northern part of India, was extracted in 70% methanol, dried at room temperature, and stored at –20 {}^{\circ }C for future use. A freshly prepared aqueous solution of ETME of different concentrations was employed into each experiment. The ETME mediated anti-tumor response in Dalton’s lymphoma was evaluated in the inbred populations of BALB/c (H2d) strain of mice of either sex at 8–12 weeks of age. The cytotoxicity of ETME in cancer cells, effects on morphology of cell and nucleus, alteration in the mitochondrial membrane potential, and level of expression of proapoptotic proteins (Bcl-2, cyt C, Bax and p53) were done using known procedures. Results: The ETME contained high content of total alkaloids (96.02 \pm 3.30 mg/100 mg), flavonoids (15.77 \pm 2.38 mg/100 mg), carbohydrate (12.71 \pm 0.59 mg/100 mg), ascorbic acid (12.48 \pm 2.59 mg/100 mg), and phenolics (0.94 \pm 0.05 mg/100 mg). Gas chromatography-mass spectrometry (GC-MS) analysis indicated the presence of 23 phytochemicals with known anticancer properties. DL cells treated with ETME exhibited significant and concentration dependent cytotoxicity. Florescent microscopy and flow cytometry of ETME treated DL cells indicated significant repair in cellular morphology and decreased mitochondrial potential, respectively. Western blot analysis displayed up-regulation of proapoptotic proteins (Bax, Cyt-c, p53) and down regulation of anti-apoptotic protein (Bcl{}_2) in DL cells treated with ETME. Conclusions: The findings of this study clearly indicated that the anticancer property of ETME was mediated via reduction in mitochondrial potential and induction of apoptotic mechanism. Further studies are warranted to explore the anticancer activities of active ingredients present in this microalga of pharmaceutical importance.