This study is conducted to compare two resin luting cements (Rely XTMARC,3M and Compolute™ESPE) on their microleakage with one composite inlay system (Filtek™ Z250 Universal Restorative Materials, 3M). Thirty conventional inlays, Class II MOIDO cavity with gingival margin I mm above the cementoenamel junction, were prepared in premolar teeth. The composite inlays were fabricated directly on the prepared teeth using layering technique. Fifteen of the inlays were cemented with RelyTMX ARC and fifteen with Compolute™ (ESPE). The specimens were kept at 370 C for 10 days before thermocycling and immersed in methylene blue 2% solution for 24 hours. The teeth were sectioned mesio-distally. The site and degree of leakage of each section was scored using a visual scoring system under a stereomicroscope at a magnification of 1.5X. Results showed that there was no significant difference in'leakage extent (p>O.05), between Rely X™ARC and Compolute™. For both materials, leakage occurred most commonly within the enamel surface and between the cement-tooth interfaces. None of the leakage occurred between inlay - cement interface. There is no significant difference in the extent of leakage between Rely XTMARC compared to Compolute™.