A serious of triply-responsive poly(N,N-dimethylaminoethyl methacrylate) (PMAEMA) containing an azobenzene group as the terminal group were synthesized by atom transfer radical polymerization (ATRP). The ATRP process of DMAEMA was initiated by an azobenzene derivative substituted with a 2-bromoisobutyryl group (Azo-Br) using CuCl/Me6TREN as catalyst and the mixture of DMA and H2O (v/v = 3:1) as solvent. The molecular weights and their distributions of the resulting homopolymers (Azo-PDMAEMA) were characterized by gel permeation chromatography (GPC). The polymers are soluble in aqueous media and exhibit a lower critical solution temperature (LCST) that alternated reversibly in response to pH and photoisomerization of the terminal azobenzene moiety. It was found that the LCST increased as pH decreased in the range of testing. Under UV light irradiation, the trans-to-cis photoisomerization of the azobenzene moiety resulted in a higher LCST, while it recovered under visible light irradiation.