Abstract. To compare the surface roughness of nanofilled and nanohybrid composite resins after polishing using a multi-step technique. 40 composite resin specimens were divided into two groups (20 nanofilled specimens using Filtek Z350 XT [group A] and 20 nanohybrid specimens using Filtek Z250 XT [group B]), prepared, and then polished. After immersion in artificial saliva for 24 hours, the surface roughness was measured with a surface roughness tester. The mean surface roughness results along with the standard deviation of group A were 0.0967 μm ± 0.0174, while the results of group B were 0.1217 μm ± 0.0244. Statistically (with p = 0.05), there were significant differences between each group. The surface roughness of a nanofilled composite resin after polishing with a multi-step technique is better than that of a nanohybrid composite resin. IntroductionNanohybrid and nanofilled resins were discovered along with the development of nanotechnology in the field of conservation dentistry, specifically in restoration [1]. Nanohybird composite resin contains a combination of micro and nano sized filler with a diameter of 0.3-1 µm and 0.02-0.05 µm, respectively [2]. Additionally, nanofilled composite resin has nano particles as filler that are both single (nanomer) and cluster (a group of nano particles called a nanocluster). The size of nano particles varies from 5-75 nm [3].A composite resin surface produced a high surface roughness level after polymerization. Roughness is mainly influenced by the composite resin filler. The larger the size and load of filler particle in a resin product, the rougher the surface [4]. Surface roughness can cause problems such as an increased retention of plaque and microorganisms, which can further develop into secondary caries and restoration failure. Surface roughness can also cause food particles to easily adhere to the restoration, causing increased discoloration. Additionally, surface roughness can wear out the opposite tooth enamel, and reduce patient comfort and satisfaction (a 0.3 µm change in surface roughness can be felt by a patient's tongue). A study showed that bacteria could adhere easily to a composite resin surface with a roughness level of 0.2 µm or more. Furthermore, a rough composite resin surface could produce a dull, unnatural clinical appearance [5].In order to resolve this problem, referring to standard operating procedure, finishing and polishing should be done after every treatment using a composite resin. Polishing is done to produce good physical properties with a smooth and shiny surface so that an esthetic restoration of good quality can be achieved