The effect of Novamin (Sensodyne Repair and Protect Paste), Hydroxyapatite (Signal Sensitive Expert-Original Paste) and Casein phosphopeptide amorphous calcium phosphate (GC MI Paste Plus) in two time intervals one week and two weeks on remineralization of enamel white spot lesions using micro-hardness test. Twenty one sound extracted human maxillary premolar teeth were selected for this study. Total of 63 pieces of adhesive tape measured 4 Χ 2 mm2 were cut and sticked on the buccal and lingual surfaces of the selected teeth to indicate two windows on the buccal surface and one window on the lingual surface of each tooth. The entire tooth including the adhesive tapes was coated with acid-resistant nail varnish. Then the adhesive tape was removed to expose the underlying sound enamel windows and the micro-hardness of each sound enamel window was measured and recorded before testing by micro-hardness machine to obtain the baseline positive control. The teeth were then immersed in demineralizing solution at pH 4.5 for 72 hours to induce caries like lesions (white spots) and the micro hardness of the demineralized enamel windows was measured and recorded for the negative control. The windows were randomly divided into three equal groups 21 windows each on7teeth according to the remineralizing agent (A): where (A1) represented demineralized enamel treated with Novamin, (A2) demineralized enamel treated with Hydroxyapatite (HAP) and (A3) demineralized enamel treated with Casein phosphopeptide amorphous calcium phosphate (CPP-ACP). Each group was divided into two subgroups according to time of application of the remineralizing agent (T) where (T1) representing application twice daily for one week and (T2) representing application twice daily for two weeks to finally get 126 measurements.