Uniform AgCl nanocubes with an average size of about 360 nm have been synthesized. Under UV illumination, a layer of silver nanoparticles with surface plasmon resonance was produced and covered the surface of AgCl particles in a short time, and the Ag/AgCl particles remained quite stable as shown in XRD patterns. The as-synthesized AgCl particles were tried for the first time as photoinitiator to polymerize N-isopropylacrylamide under UV-irradiation, and a high efficiency and conversion rate were realized. The structure of the polymers was studied by FTIR spectrophotometer. The results of turbidimetric method showed that the polymers were temperature sensitive and their lower critical solution temperature was about 33 °C. The effects of photoinitiators concentration, monomers concentration, and irradiation time on the polymer yield were investigated. The reaction mechanism was discussed by using salicylic acid as scavengers of hydroxyl radicals and conducting the reaction under oxygen atmosphere, respectively. The results proved that hydroxyl radicals were essential to chain initiation.