Resin composite is the most popular tooth-colored material for the dental restoration. The polymerization shrinkage is an unavoidable disadvantage of this material which is associated with the gap formation and the secondary caries. Bonding system is used to eliminate these problems. However, the gingival margin of the proximal cavity remains the most common area found the restorative defects. An open sandwich technique has been suggested to address this problem. The aim of this study is to evaluate the degree of nanoleakage and adaptability of different lining materials in open sandwich technique. The slot cavities were prepared on the proximal surface of teeth with the gingival margin 1 mm below the CEJ. The teeth were divided into 5 groups (n=5): group I a flowable resin composite, group II a bulk fill flowable resin composite, group III a resin modified glass ionomer cement, group IV and V no lining material. Samples in the group I-III and V were restored with nanofilled resin composite while group IV were restored with bulk fill resin composite. All groups were thermocycled, processed with silver nitrate solution and observed under SEM. The silver nitrate deposited entire thickness of hybrid layer, in the dentinal tubules and on the resin tags in group I, II, IV and V. In group III, it deposited within the modified hybrid layer. The silver nitrate deposition was highest in group V (70.44 %) while the group II (55.29 %) was the lowest. The gap formation was found in almost all outer 1/3 of samples. The width of gap was different among materials. In the conclusion, the type of lining materials had an influence on the degree of adaptability to dentin while it did not effect on nanoleakage of bonding system. The bulk fill resin composite could improve the adaptability of the restoration to cervical dentin margin.