The purpose of this study was to compare the microleakage pattern of glass ionomer with resin restoration in microleakage pattern of primary and permanent teeth. Microscopical observation of interface between tooth structure and restoration was also performed. 80 and 8 sound molar teeth were used for the microleakage test and SEM study respectively. Data were analyzed statistically using ANOVA test and/or t-Test. The results of the present study were as follows: 1. According to the result of microleakage pattern between primary and permanent tooth, primary tooth generally showed more micro leakage than permanent tooth in all groups (p<.05). 2. In the resin-filled groups, occlusal margin was shown to have more microleakage than gingival margin(p<.05). Whereas the glass ionomer-filled groups showed no statistically significant differences between them(p>.05). 3. No statistically significant differences in microleakage could be found between two different resin groups(p>.05), while Fuji II LC group showed less microleakage than Ketac-Fil group(p>.05). 4. The various type hybrid layer was evident under SEM in resin-filled groups both in primary and permanent teeth with generally thicker layer in primary group. Among glass-ionomer group, Fuji II LC group showed more intact adhesion to tooth surface than Ketac-Fil group