The limitation for the biomedical application of porous organic polymers (POPs) is the big size and poor dispersibility in aqueous media. Herein, a nanoscale metal–organic framework (MOF)@POP composite, named UNM, has been synthesized by epitaxial growth of the photoactive porphyrin-POPs (H2P-POP) on the outer surface of amine containing UiO-66 (UiO-AM). After the growth of POPs, the crystallization, pore structure, and size distribution of UNM are retained well. The formed UNM possesses a small size of less than 200 nm and could be internalized by cancer cells. Such light-activated UNM exhibits efficient ability to generate 1O2 under various experimental conditions, which can be further applied for PDT efficacy. The present work demonstrates the great potential of nanoscale porous polymers in biomedical fields and cancer treatment.