Aims: This study aims to compare and evaluate the effect of two remineralizing agents: fluoride varnish and silver diamine fluoride solution on the surface microhardness of enamel of primary teeth. Materials and methods: A total of (150) primary anterior teeth were used in the study. Enamel blocks were prepared and divided into three groups: Fluoride varnish n(50), silver diamine fluoride n(50) and the control group of deionized water n(50), then introduced into PH cycle. Microhardness of enamel blocks was measured using Vickers microhardness tester machine (OTTO Wolpert−WERKE GMBH) before and after the PH cycle. Results: There were highly statistically significant differences among study groups after PH cycle and there were a decreasing in surface microhardness in all groups due to the demineralization, but the least reduction in surface microhardness belonged to silver diamine group followed by fluoride varnish group. Conclusions: Silver diamine fluoride was significantly better than fluoride varnish in preserving enamel's hardness and resistant to demineralization.