Sensitizing the antitumor activity of monofunctional Pt-II complexes is a reliable approach to developing antitumor agents different from the classic Pt-based drugs. Considering the poor intracellular accumulation of monofunctional Pt-II complexes, in this study, the photosensitizing monofunctional Pt-II complex Pt-BA was derived from a weak BODIPY (boron-dipyrromethene)-derived photosensitizer BA, with the purpose to improve its antitumor cytotoxicity via enhancing its intracellular accumulation with a short time photo-irradiation. Photoinduced reactive oxygen species (ROS) determination indicated that the all center in Pt-BA is able to improve the photoinduced ROS production ability of BA, which makes Pt -BA a mild photosensitizer. Fluorescence imaging disclosed that dark incubation makes Pt -BA accumulate mainly on the surface of cell membrane, and the later short time photo -irradiation (5 min) promotes distinctly the intracellular accumulation of Pt-BA, which has been confirmed by inductively coupled plasma-mass spectrometry determination. Flow cytometric Annexin V-FITC assay indicated that the short time irradiation of Pt-BA induces in situ the cell membrane damage, which might finally enhance the intracellular accumulation of this monofunctional complex. 3-(4,5-Dirnethylthiazol-2y1)-2,5-diphenyltetrazolium bromide assay confirmed that the short time photo-irradiation promotes distinctly the antitumor cytotoxicity of Pt -BA against MCF-7, SGC-7901, A549, and HeLa cell lines. The photopromoted antitumor activity of Pt -BA implies that modifying monofunctional Pt-II complex as a mild photosensitizer to promote its cell accumulation is a useful approach to sensitizing the antitumor activity of monofunctional Pt-II complex and renders the possibility of monofunctional Pt-II prodrugs, for precise chemotherapy via only short time photoactivation.