The aim of this study was to evaluate the effect of fluoride varnish application on enamel decalcification. Eighty bovine enamel blocks divided randomly into 4 groups. Group I is the control group. Group II was treated with the APF gel and washed after 4 minutes. Group III and IV was treated with Fluor $Protector^{(R)}$ and $CavityShield^{TM}$ and washed after 1 minutes. Decalcification were created by placing all specimen into artificial acidic solution(pH 4.0). Then the optical density of the lesions were measured by visible light fluorescence and the lesion depths were measured. The results were : 1. The optical density of group II was higher than group I but lower than group III, IV(p<0.05) and there was no difference between group III, IV(p>0.05) at 48 hours. 2. The optical density of group IV was highest at 72 hours(p<0.05). 3. Mean lesion depths were $205.36{pm}42.85{mu}m$ and $210.81{pm}44.60{mu}m$ in group I, II but no significant difference between two groups(p>0.05). 4. Mean lesion depths were $80.03{pm}21.66{mu}m$ and $77.46{pm}27.72{mu}m$ in group III, IV but no significant difference between two groups(p>0.05). Fluoride varnish treatment resulted in a significant reduction in lesion depth compared with APF gel. Fluor $Protector^{(R)}$ and $CavityShield^{TM}$ provided the similar effect.