Utilizing zinc acetate as precursor, and monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) as stabilizers, respectively, ZnO nanoparticles with uniformly distributed grains were synthesized by sol-gel method at different sintering temperatures. Analysis of the degradation of methyl orange by photocatalysis shows that utilizing MEA as the stabilizer and 550°C as the sintering temperature results in smaller grain size, greater surface-to-volume ratio, and a density of surface defects suitable for a photocatalyst. The greatest photocatalytic degradation of methyl orange was achieved under UV irradiation. Based on our microstructural analysis and photocatalysis, the microstructure of ZnO particles and, in turn, their photocatalytic effect are affected significantly by the stabilizer type and the sintering temperature.