ABSTRACTIntroduction: The surface hardness of enamel is affected by demineralization and remineralization of enamel. Demineralization can cause the enamel surface hardness to decrease. Carbonated drinks are acidic drinks which can lower the pH of the oral cavity and cause damage to the enamel. Lost tooth minerals can be restored with remineralizing materials, one of which contains calcium. Natural materials that can help remineralization are calcium carbonate (CaCO3) which can be found in several animal shells such as marine materials, pearl snails and eggshells. Duck eggshell is one of the household wastes which is high in calcium which consists of 94% calcium carbonate. The purpose of this study is to analyze differences in enamel surface hardness between soaking carbonated drinks and application of duck eggshell paste remineralization material. Methods: This type of research is a true experimental laboratory with a pretest-posttest research design with control group design. The study sample was 8 post-extraction premolars that matched the inclusion criteria. The samples were divided into two groups which were previously soaked in carbonated drinks for 15 minutes. Group I: duck eggshell paste and group II: pasta without duck eggshell which was applied for 3 minutes 2 times a day for 14 days. Hardness measurement using Vickers hardness tester. Results: based on data analysis using paired t-test. Enamel surface hardness after immersion in carbonated drinks (mean=327.50 SD=23.33). The enamel surface hardness increased after application of duck eggshell paste (mean=467.50, SD=14.15) p=0.001. The control group also increased after the application of pasta without duck eggshell (mean=429.40 SD=29.01) p=0.002. Conclusion: There is a difference in the hardness of the enamel surface after being soaked in carbonated drinks and after the application of duck egg shell paste. KEYWORDSdemineralization, enamel surface hardness, carbonated drinks, duck egg shell paste, remineralization.