Purpose: To study the effects of cigarette smoke (CS) on the discoloration of dental resin composite compared with the aerosol from a heat-not-burn tobacco product, the Tobacco Heating System 2.2 (THS2.2). Methods: A total of 60 discs were prepared from three commercial resin composites: Durafill VS (DVS), Filtek Supreme Ultra (FSU) and Tetric EvoCeram BulkFill (TEC). Twenty discs of each composite were divided into two groups and exposed to CS from 20 reference cigarettes (3R4F) or aerosol from 20 THS2.2 tobacco sticks per day for 3 weeks. Color, gloss and surface roughness of the composite discs were measured at baseline and after exposure and brushing with toothpaste at 1, 2 and 3 weeks. Results: Color differences from the baseline (ΔE) were on average 27.1 (±3.6) in 3R4F and 3.9 (±1.5) in the THS2.2 group after 3 weeks of exposure (P< 0.0001). TEC (30.4±1.4 and FSU (28.0 ±2.5) exhibited more discoloration than DVS (23.0±1.2) in the 3R4F group (P< 0.0001). FSU (2.6 ±0.5) showed significantly less discoloration than TEC (5.3±1.5) in the THS2.2 group (P< 0.0001). Surface roughness of resin composites was not affected by either CS or THS2.2 aerosol, while surface gloss increased in the composite discs with more severe discoloration. Clinical significance: Cigarette smoke caused significant discoloration of dental composite resins. Reducing or eliminating the deposits derived from combustion of tobacco has the potential to minimize the impact of smoking on the color of composite resin restorations.