This in vitro study evaluated the effect of removing smear layer and applying adhesive on the marginal adaptation of amalgam fillings to cavity walls. Three groups were established, cavities in group 1 were exposed to 10% EDTA (pH7.4) for 1 minute to remove smear layer before amalgam condensation; cavities in group 2 were also subjected to EDTA, then Miradapt adhesive was applied on the walls, finally amalgam condensed into cavities before the adhesive set; cavities in group 3 received no special treatment before amalgam condensation. After thermocycling, all teeth were subjected to SEM and image analyser. Results showed: Space between restorations and tooth structure in group 1 was 6.31 microns, space in group 2 with adhesive was 3.49 microns and micromechanical interlocking was observed while space in control group was 14.22 microns. Difference among the three groups was statistical significant. It was indicated that removing smear layer and using adhesive resin significantly improved the adaptation of amalgam to cavity walls.