Context: Evaluation of microleakage is important for assessing the success of newer restorative materials. Aim: To evaluate & compare microleakage in deep class II restorations using open-sandwich technique with two different liners at tooth-liner interface & linerrestoration interface. Materials & Method: Forty non-carious premolars were selected and randomly divided into two groups (n=20). A mesio-occlusal class II cavity preparation was made with the cervical margin 0.5-1mm below the cemento-enamel junction in all the samples. Zirconomer was used as base in Group I and Resin modified glass ionomer cement (RMGIC) in Group II followed by composite resin restoration in both the groups. Teeth were then subjected to thermocycling in 5°C and 55°C water baths. Root apices were sealed and samples were immersed in 0.5% methylene blue dye. Teeth were sectioned in mesio-distal direction and observed under stereomicroscope. The data was collected and results were analyzed using Mann Whitney U test. Results: Zirconomer showed significantly higher microleakage (p< 0.05) as compared to RMGIC at tooth and liner interface. Statistically non-significant difference (p>0.05) was observed between the groups at the liner-restoration interface. Conclusion: Resin modified glass ionomer cement proved to be better than Zirconomer as liner in deep class II preparations