The aim of this study is to compare the effect of two resin infiltration systems on microhardness and surface roughness of demineralized enamel before and after an acidic challenge. A total of 40 caries-free human maxillary molar teeth was used in this study. Four standardized 3×3 mm2 windows were marked onto each tooth; two in the mesial surface and two in the distal surface, and the rest of tooth was covered with acid resistance nail varnish. Then, teeth were immersed in demineralizing solution at pH 4.5 for 72 hours at 35 ºC.Each tooth comprised 4 groups; Group 1- represents untreated sound enamel surface (Positive Control), Group 2- represents artificially demineralized enamel surface (Negative Control), Group 3- represents of Icon resin infiltrant (DMG America, Englewood) to demineralized enamel, while Group 4- represents of Single Bond Universal adhesive (3M ESPE, USA) to demineralized enamel. For all groups, micro-hardness was assessed using Vicker`s micro-hardness test and surface roughness was tested using Optical profilometry. Group 3 and group 4 were further subjected to acidic challenge then further assessed using the same methods. The results for micro-hardness revealed that Icon resin infiltrant and Single Bond Universal adhesive showed significantly higher mean micro-hardness than Negative Control, but significantly lower mean micro-hardness than Positive Control. However, an insignificant difference was found between Icon and Single Bond Universal adhesive. While, after the acidic challenge, Icon resin infiltrant showed significantly higher mean micro-hardness than Negative Control. However, Single Bond Universal adhesive showed insignificant difference than Negative Control. In addition, both treatments showed significantly lower micro-hardness than Positive Control with insignificant difference between both treatments.The results for surface roughness showed that Single Bond Universal adhesive and Icon resin infiltrant revealed significantly lower mean surface roughness than Negative Control, but significantly higher mean surface roughness than Positive Control. However, an insignificant difference was found between Icon and Single Bond Universal adhesive. While, after acidic challenge, both Single Bond Universal adhesive and Icon resin infiltrant showed insignificant mean surface roughness than Negative Control. In addition, both treatments showed significantly higher mean surface roughness than Positive Control with insignificant difference between them.