B ackground: Dental erosion can affect the dental demineralization due to the pHlevel that is below the critical pH of 5,5 resulting a decrease in dental enamelhardness. Remineralization is needed to bring back the mineral loss.Hydroxyapatite can remineralize the tooth. Objectives: To analyse theeffectiveness of 4 wt% hydroxyapatite paste on dental enamel hardness aftererosion for 7 and 14 days. Method: 20 maxillary premolars were divided into 4groups. Group A1 was applied with 4 wt% hydroxyapatite paste for 30 minuteseach day for 7 days, group A2 was applied with 4 wt% hydroxyapatite paste for 30minutes each day for 14 days, group B1 was immersed with artificial saliva for 7days, and group B2 was immersed with artificial saliva for 14 days. All groups wereimmersed with artificial saliva and placed inside an incubator for 24 hours at 37°C.Dental enamel hardness was measured with Vickers Hardness Tester (ShimadzuHMV G-21 Series). Dental enamel hardness data was analysed with GLM RepeatedMeasure ANOVA test (p<0,04) and One-way ANOVA test (p<0,05). Results:Dental enamel hardness number after 4 wt% hydroxyapatite paste applicationshows significant difference than untreated group, which was immersed in artificialsaliva. Dental enamel hardness number after 4 wt% hydroxyapatite pasteapplication for 14 days shows significant difference than 4 wt% hydroxyapatitepaste application for 7 days. Conclusion: 4 wt% hydroxyapatite paste applicationfor 14 days results in an increase in dental enamel hardness as in the normalcondition of dental enamel before erosion.