© 2022. All Rights Reserved.Objectives: The aim of this in-vitro study is to investigate discoloration of the composite resins with different characteristics which were colored by immersing in coffee, kept in mouthwashes with and without hydrogen peroxide. Materials and Methods: In this study, 18 samples (6 mm x 2 mm) pre-heated bulk-fill (Viscalor Bulk -(VIS)), dual-cured (Fill Up!-(FUP)) bulk-fill and a microhybrid composite resin (G-aenial posterior-(GCP)) were prepared. After the samples were kept in distilled water for 24 hours, baseline colour measurements were performed with a spectrophotometer. ΔE001 color measurements were made of the samples immersed in coffee for 7 days. The samples were divided into two groups to be kept in mouthwashes with hydrogen peroxide (Crest 3D White) and without hydrogen peroxide (Listerine Advance White) (n=9). ΔE002 color measurements were applied after kept in whitening mouthwashes for 24 hours. Discoloration were calculated with the CIEDE2000 formula. Data were statistically analysed with One-way ANOVA and post hoc tukey tests. Results: For samples immersed in coffee, while statistically highest AE values were obtained in GCP (7.30) group, there was no difference between VIS (3.30) and FUP (3.01). Statistically significant colour reduction was observed in VIS and FUP samples kept in both mouthwashes. GCP samples showed colour change above the clinically acceptable threshold (ΔE<2.25). Conclusions: A decrease in discoloration for all materials was found as an effect of whitening mouthwashes. However, GCP showed clinically unacceptable discoloration after immersed in coffee or mouthwashes. Both whitening mouthwashes provided effective whitening for VIS and FUP groups.