Purpose : To compare nanoleakage in permanent molars restored with bulk-filling, snowplow and injection-molded composite application techniques using a universal adhesive with two different etching modes. Materials &Methods: A total of twenty four human permanent molars were used. Class II box was prepared on the proximal surfaces of molars. Forty eight specimens were randomly divided into three main equal groups according to resin composite application techniques, bulk-filling, snowplow and injection-molded techniques. Each group was further subdivided into two subgroups according to etching mode; etch and rinse mode and self -etch mode. Each specimen was sectioned mesiodistally and immersed in 50% freshly prepared silver nitrate solution followed by washing under running water and were kept for 8 hours in a photo-developer solution. The specimens were analyzed in (ESEM) and the amount of silver nitrate within the adhesive layer, hybrid layer and the resin tags was analyzed. Results: There was a statistically significant difference in nanoleakage regarding to the three different composite application techniques. Bulk filling and injection molded techniques had mean values that are close to each other, while these mean values were greater than the ones snowplow have. There was a statistically significance difference between etch and rinse mode and self-etch mode. Also, the effect of etching mode on nanoleakage was more than twice as much as that of composite application technique. Conclusion Using the “snowplow" technique with etch and rinse mode of universal adhesive, can decrease nanoleakage rate, moreover etching mode could influence the nanoleakage of universal adhesives.