This study was carried out to evaluate the effect of Er, CR: YSGG LASER, fluoride varnish and their combination on the microhardness ofdemineralized enamel white spot lesion before and after pH cycling.Fifteen freshly extracted intact human teeth were divided into six subgroups. The coronal portion of each tooth was divided into four standardized windows 3x3 mm either on the buccal or the lingual surface. All specimens were demineralized in a demineralizing solution for three days except the positive control group. The sixty specimens were divided to six groups. The first group I1: positive control (sound enamel), I2: negative control (demineralized enamel), I3: Er: chromium LASER, I4: fluoride varnish, I5: Er: chromium LASER and then fluoride varnish, I6: fluoride varnish and then Er: chromium LASER. The microhardness was measured for all these six groups. Then, all groups were subjected to a pH cycling model then the microhardness was measured to all the specimens. In the present study there was no statistically significant difference between all the tested groups before pH cycling. After pH cycling, there was a statistically significant difference between the combination of LASER and then fluoride group which showed the highest statistically significant mean microhardness value and the demineralized (negative control) group which showed the lowest statistically significant mean microhardness value.