Introduction:Arginine is a natural component of human saliva, which has recently been incorporated in dentifrices treating teeth sensitivity and acts as a protective factor against caries. Aim of the study: This study evaluated the effect of two different concentrations of arginine; 2.5% and 8% on fluoride uptake by demineralized enamel surfaces. Methods:80 specimens obtained from 40 human premolars were divided randomly into 4 equal groups (n=20 per group): (GI=negative control), (GII=positive control) treated by sodium fluoride (NaF500 ppmf), group III treated by combination of sodium fluoride solution (NaF 500 ppmf)+arginine solution (2.5%) and group IV treated by combination of sodium fluoride solution (NaF 500 ppmf)+arginine solution (8%). Microhardness was tested using Vickers microhardness test, in addition to imaging using environmental scanning electron microscope (ESEM) and minerals content was assessed using energy dispersive X-ray spectroscopy (EDX). Statistical analysis was performed utilizing Kolmogorov-Smirnov and Shapiro-Wilk tests for normality of data, Levene's tests for homogeneity and one-way ANOVA with Bonferroni post hoc tests for the evaluation of statistical significance among the groups. Results: Highest mean microhardness was in group III (370.58±12.14) and group IV (370.22±8.24). An increase in mineral density was found in group IV followed by group III, then group II and group I as revealed by ESEM. Data analysis showed increase in fluoride concentration in group III followed by group IV, group II and group I with a mean value (17.59±1.33), (14.62±1.91), (13.57±2.29) and (14.32±2.13) respectively. Conclusion: Fluoride uptake of demineralized enamel is increased when using both concentrations of arginine (2.5% and 8%). Arginine modulates areas of mineralized deposits and overall refinement of enamel ultrastructure.