Gold nanostars (GNSs), were synthesized and coated with N-(3-aminopropyl) methacrylamide hydrochloride (PA) in order to functionalize their surfaces by amine groups as well as to investigate the production of singlet oxygen (1O2). The singlet oxygen production by the large sized GNSs with multi-tips seems to be superior to that by the small GNSs with fewer tips. In combination with methylene blue (MB+), the functionalized GNSs could increase the singlet oxygen production of MB+ after 1 h of LED750 irradiation. Only PA-coated GNSs could catalyze the oxidation reaction of 5-aminolevulinic acid (ALA) for the singlet oxygen production.