Abstract : A significant factor that determines the effectiveness and endurance of restorative materials in the oral cavity is their ability to adhere to cavity walls. The objective of the current study was to determine and compare the microleakage of restorations made with newer materials ORMOCER and Nanocomposite resin with that of Conventional microfilled composites. For an in-vitro study, 30 premolars were used and prepared with Class II cavities. They were randomly divided into three groups of 10 teeth each, based on the restorative material used. Group I was filled with a Conventional Microfilled Composite (Filtek Z250 Universal restorative+ DX. Bond, which is a total etch light cure adhesive System) Group II with Nanocomposite (Filtek Supreme XT by 3M ESPE, St Paul, MN, USA + Scotchbond Multipurpose, 3M ESPE) and Group III with ORMOCER (Admira Fusion Voco + Admira Bond). The microleakage was assessed by sectioning the teeth and examining them under a stereomicroscope. The statistical significance was established using the Chi-square test, with a p-value of less than 0.05 being considered significant. The average dye penetration in groups I, II, and III was found to be 0.57 mm, 0.24 mm, and 0.05 mm, respectively. The distinction was appreciable. (P ≤ 0.05). Compared to Nanocomposite and Conventional microfilled composites, ORMOCER materials demonstrated the least microleakage.