Abstract: Objective To investigate the anti-tumor effects of photodynamic therapy(PDT) using Photodithazine, a chlorin e6 derivatives, as photosensitizer(PS) on mouse B cell lymphoma both in vitro and in vivo. Methods After treated with various concentrations (0.125-1.0 μg/ml) of PS, A20 cells were illuminated with 6.25 J/cm2 of laser wavelength (662 ± 3) nm. WST-1 assay was performed to detect the cell proliferation, electron microscopy was used to observe morphological changes, and flow cytometry(FACS) was applied to detect the apoptosis rate and the expression of B cell specific antigen-CD45R. We established lymphoma animal model by subcutaneously injecting A20 cells into Balb/c mice. Tumor growth was recorded after PDT intervening in vivo. The expressions of P53, P21 and Bax in tumor tissue were detected by Western blot. Results After PDT for 24 h, the growth of A20 cells was inhibited in the group with > 0.50 μg/ml of PDT(P<0.05), moreover, there was significant inhibition in the group with 0.25 μg/ml of PDT after 48 h (P<0.01). Apoptotic and necrotic cells were detected under the microscope. We successfully established lymphoma animal model and tumor growth was inhibited by PDT in vivo(P<0.05). P53, P21 and Bax were highly expressed in tumor tissues which accepted PDT in vivo. Conclusion Photodithazine/PDT has anti-tumor effects on A20 lymphoma both in vitro and in vivo.