Abstract:[Objective] pH buffering capacity (pHBC) highlights the capacity of a soil to resist changes in soil solution pH as the concentration of protons (H+) changes. The most widely used method for determining soil pHBC is acid-base titration. The soil pHBC can be calculated from a buffering curve showing the relationship between H+ concentration and soil solution pH. Nevertheless, the fitting method of titration data has a penetrating influence on the result of soil pHBC and needs to be investigated.[Method] In this study, acid-base titration curve was adopted to measure the pHBC of 38 acid purple soils. Four fitting methods (polynomial curve fitting of all data (PA), linear fitting of data between two inflection points (LT), polynomial curve fitting of acid titration data (PAT), and linear fitting of acid titration data (LAT)) were used to fit the soil acid-base titration data and the pHBC estimated from the different fitting methods.[Result] The pHBC obtained by the different fitting methods was different. Also, the different fitting methods produced different R2 for the fitting equation. The R2 obtained by LAT was lower than that of the other three fitting methods, which result in lower accuracy of the soil pHBC calculated by linear fitting of acid-base titration data. More so, PA produced the best fit for the acid-base titration data. The correlation between soil pHBC calculated by the different fitting methods and soil exchangeable cations(r1) or effective cation exchange capacity (ECEC, r2) was as follows:PA(r1=0.486**, r2=0.525**) > LT(r1=0.223, r2=0.245) > PAT(r1=0.183, r2=0.220)> LAT(r1=-0.219, r2=0.002). There was a significant positive relationship between soil pHBC calculated by the PA method and soil exchangeable cations or ECEC. This revealed that the pH buffering ability of the tested soils at current pH value was mainly controlled by exchangeable cations and weathering of silicate.[Conclusion] Given the importance of soil pHBC, an accurate method for its measurement is essential. Thus, estimating pHBC of soils by fitting the acid-base titration data using PA is a reliable method.