Light has several advantages as the stimulus for a triggered drug release. Currently, the applications of phototriggered drug-release devices (PDDs) are largely limited by two factors: the limited tissue penetration and detrimental effects caused by excitation light (ultraviolet or visible light). To address this disadvantage, this study developed nanocomposites based on upconversion nanoparticles (UC), which could convert near-infrared light to ultraviolet-visible light and trigger drug release. By loading UC and doxorubicin (DOX) into photoresponsive copolymer PEG-NMAB-PLA (PNP), near-infrared responsive copolymer upconversion nanocomposites (PNP-DOX-UC) were constructed. We proved that PNP-DOX-UC showed the fast release and strong cytotoxicity under near-infrared irradiation in vitro. The therapeutic efficacy study indicated that PNP-DOX-UC+ hv had the enhanced antitumor efficiency. In the study, UC becoming an internal ultraviolet-visible light source for near-infrared excitation develops an applicable and efficient approach to meet the requirements for UV/vis excitation, which is a major disadvantage in photosensitive materials developed for pharmaceutical and biomedical applications.