Background: The ion activity product for hydroxyapatite (Ip HA ) is a comprehensive parameter reflecting pH, calcium and phosphate ion concentration in saliva which govern the degree of saturation with respect to the dissolving tooth mineral. The aim of this study was to evaluate the relationship between quantitative assessments of salivary buffering capacity and Ip HA in relation to cariogenic potential. Methods: Stimulated whole saliva was collected from 33 patients, and the initial pH of samples was measured using a handheld pH meter. Then samples were titrated with 0.1 N HCl to evaluate buffering capacities and divided into three groups (high, medium and low). After measuring concentrations of calcium and phosphate ions in the samples, Ip HA was calculated using the values of the ion concentrations and pH. Differences in the mean pH values, the concentrations of calcium, phosphate ions and log[Ip HA ] among three groups were analysed using the Kruskal Wallis and the Mann-Whitney nonparametric test, p < 0.05. Results: After HCl 50 lL titration, there were statistical differences of the mean pH and Ip HA among each buffering capacity group. Moreover, after 50 lL HCl titration, there was an excellent correlation between the buffer capacity and log[Ip HA ]. Conclusions: The pH change for saliva after HCl titration has a significant influence on the rate of Ip HA .