For more esthetic treatments the use of composite in molar areas are increasing. But polymerzation shrinkage that cause marginal leakage and cuspal deflection has been the problems of composites. The purpose of this study is to compare the effect of low intensity curing and polishing period on marginal leakage. Cavities were prepared on the buccal or lingual surface of forty five sound extracted human teeth and etching, application of bonding agent and filling of composite was done. Group 1 was light cured at intensity of 600$mW/cm^2$ for 41 seconds and polished. Group 2 was light cured at intensity of 300$mW/cm^2$ for 2 seconds and polished and after polishing it was light cured for 40 seconds at 600$mW/cm^2$. Group 3 was light cured at intensity of 300$mW/cm^2$ for 2 seconds and waited for 5 minutes and after curing at 600$mW/cm^2$ for 40 seconds polishing was done. The specimens were thermocycled at $5^{circ}C$ and $55^{circ}C$ for 1000 cycles and immersed in 2% methylene blue solution for 24 hours. Composite-tooth interface was examined under stereobinocular microscope for dye penetration. The results were as follows : 1. Group which were cured at low intensity and polished after curing at high intensity showed less marginal leakage than group which were cured at high intensity for 41 seconds(p<0.05). 2. Marginal leakage between group which were cured at low intensity and polished immediately and group which were cured at high intensity for 41 second were not significantly different. Light curing at low intensity can reduce marginal leakage but polishing immediately after curing at low intensity for short time can affect marginal leakage.