The purpose of this in vitro study was to compare the bleaching effect and the surface change according to three bleaching agents (Rembrandt, Natural White, Hi-Lite). Teeth were stained by artificial food colorants for 6 weeks and bleached for 4 weeks. The teeth were evaluated with spectrophotometer after bleaching on the 1st week and on the 4th week. The surface change of enamel was evaluated under SEM after exposure to 3 agents for 1 and 24 hours. The results were as follows : 1. All groups showed increased Lightness difference after bleaching. 2. After 1 week, only Rembrandt group showed significant bleaching effect compared to control group. 3. After 4 weeks, Rembrandt group and Hi-Lite group showed significant bleaching effect compared to control group. 4. SEM evaluation revealed that enamel surface underwent considerable change after 24 hours. Scratch disappeared and smooth surface was shown.