Aim: The present study aimed to evaluate the surface roughness and microbial adhesion of Alkasite resinbased composite versus bioactive Giomer after simulated tooth brushing. Material and Methods: A total of forty-eight disc shaped specimens of giomer and alkasite resin based composites were set using Teflon split mold (1.5 × 8.5 mm) (n=6), finished and polished then the top surface of the specimens was subjected to simulated toothbrushing immediately. The specimens were randomly allocated into two groups; twentyfour each from both materials, for surface roughness (Ra) and microbial adhesion assessment then each group was subdivided into two groups according to time of assessment. The surface roughness was tested immediately (T1) and after three months of storage in distilled water (T2) by profilometer in micrometres. Microbial adhesion was tested after 24hours (Ta) and 48hours (Tb) of incubation using colony forming units. Selected samples from each subgroup were examined by Scanning Electron Microscopy (SEM) to observe the surface before and after storage time. Data were analyzed and tabulated using two-way ANOVA. Pvalues were adjusted for multiple comparisons using Bonferroni correction. Spearman's rank-order correlation was used for coefficient Correlation analysis. The significance level was set at (p<0.05). Results: Alkasite showed a statistically significant higher surface roughness and microbial adhesion than Giomer at different times (p = 0.001). Conclusions: Giomer had better performance in surface roughness and bacterial adhesion than Alkasite. Bacterial adhesion is strongly dependent on the surface roughness of restorations.