The aim of this study was to compare the percent of weight loss of enamel, calcium ions concentration, and changing in the pH of various solutions simulated oral conditions. Two hundred and forty six bovine enamel slabs of 5.0x7.0x1.0 mm3 and weight 110±30 mg each were prepared and randomly divided into 5 groups of solutions: 0.07 M lactic acid (Group 1), artificial saliva (Group 2), lactic acid+artificial saliva (Group 3), lactic acid+artificial saliva+hydroxyapatite crystal (Group 4). The enamel specimens in Group 5 were infiltrated with resin before soaking in lactic acid+artificial saliva. Each specimen was immersed in 10 ml each of the solutions for 5 min, 15 min, 30 min, 1 h, 5 h, 24 h, 3 day, and 7 day (n=6). The tested specimens were ultrasonically cleaned in deionized water for 1 min and air-dried all surfaces for 1 min. The weight was measured and calculated to percent of weight changing. The solutions were detected for the calcium ions concentration and the pH value. Analysis results from one way ANOVA showed that Group 1 had the highest percent of weight loss, statistically significant difference between group solution and time intervals were revealed. Percent of weight loss in Group 3 was significant difference with Group 2 all the time intervals. No significant difference in percent of weight change between Group 2, 4 and Group 2, 5 was found in the time of 1 h and 5 h, respectively. Significantly increased in the calcium ions concentration of Group 1 and 3 all the time intervals were revealed. Group 2 was significantly decreased of the calcium ions concentration in 7 day. Statistically significant difference in the calcium ions concentration of Group 4 and Group 5 was found in 3 day and 24 h, respectively. The pH of each group solutions was significant difference all time intervals, except Group 3 and 5 no significant difference were revealed in 5 h. During the testing time, the pH values of Group 2, 4, and 5 were no significant difference. It can be concluded that saliva could not protect the enamel demineralization, while synthetic hydroxyapatite crystal and hybridized layer protected enamel from acid demineralization in 1 h and 5 h, respectively.