Statement of the Problem: Acidic foods and drinks can erode composite resins. Silorane-based composite is a new low shrinkage composite with higher hydrophobicity which might resist the erosive effect of beverages.Purpose: The aim of this study was to determine the effects of 100% orange juice and non-alcoholic carbonated beer on microhardness of a silorane-based composite in comparison with two methacrylate-based composite resins.Materials and Method: Ninety disc-shaped composite specimens were fabricated of Filtek P90, Filtek Z350 XT Enamel and Filtek Z250 (3M-ESPE) (n=30) and randomly divided into 3 subgroups of 10.Group 1 was immersed in distilled water, group 2 in 100% orange juice, and group 3 in non-alcoholic beer for 3 h/day. Primary, secondary and final Vickers microhardness tests were performed at the beginning of the study and 7 and 28 days later. Surface of 2 specimens in each group was evaluated under scanning electron microscope on day 28. Data were analyzed using repeated measures of ANOVA model (α=0.05).Results: The primary and secondary microhardness of P90 was significantly lower than that of Z350, and Z250 (p< 0.001). Microhardness of Z350 was also lower than that of Z250 (p= 0.002). On day 28, microhardness of P90 was lower than Z250 and Z350 (p< 0.001); however, microhardness values of Z250 and Z350 were not significantly different (p= 0.054). Microhardness of specimens subjected to non-alcoholic beer was significantly lower than that of controls (p= 0.003). Meanwhile, the microhardness value of resins in orange juice was somewhere between the two mentioned values with no significant difference with any of them (p> 0.05).Conclusion: Although 28 days of immersion in 100% orange juice and non-alcoholic beer decreased the microhardness of all specimens, P90 experienced the greatest reduction of microhardness and non-alcoholic beer had the highest effect on reducing microhardness.