Background: Enamel demineralization is a common and undesirable side effect of fixed appliance orthodontic treatment. Many sudies showed that the prevalence varied between 2–96%. There are many ways to prevent demineralization and increased remineralization such as oral hygiene instruction and by topical application such as acidulated phosphate fluor (APF) casein phospo peptide-amorphous calcium phosphate (CPP-ACP), casein phospo peptide-amorphous calcium phosphate plus (CPP-ACPF). Purpose: The purpose of this in-vitro study was to evaluate the efficacy of various topical agents to prevent enamel demineralization. Methods: Fourty extracted human premolars were allocated to 1 of 4 groups: 1.23% APF gel; 10% CPP-ACP paste; 10% CPP-ACPF paste; and untreated control. All samples were subjected to pH cycling treatment for 12 days through a daily procedure of demineralization solution with pH 4 for 6 hours and remineralization solution with pH 7 for 18 hours. Microhardness testing were done before and after pH cycling and the delta hardness values were determined. Results: APF, CPP-ACP and CPP-ACPF application significantly prevent lowering of enamel microhardness value compared with untreated control group. Kruskal-Wallis, ANOVA, Mann-Whitney U, Tukey and Bonferroni Post-Hoc multiple comparison test showed significant difference between mean delta microhardness value of CPP-ACPF and CPP-ACP group with APF group, but there is no significant difference between mean delta microhardness value of CPP-ACPF and CPP-ACP group. Conclusion: APF, CPP-ACP and CPP-ACPF prevent enamel demineralization. CPP-ACP and CPP-ACPF prevent demineralization more than APF.