Abstract: Sedimentary organic carbon stable isotopic ratios can be measured by coupled elemental analyzer and stable isotope mass spectrometer (EA-IRMS). The acidification pretreatment of the samples, however, can influence the accuracy of the results. In this paper, we presented the results of comparison of two most commonly used pretreatment methods:acid rinse and hydrogen chloride fumigation, on the influence of the sedimentary organic carbon stable isotopic measurement. The best condition of acid rinse method was that the samples treated by 1 mol/L HCl for 8 h, then the sedimentary inorganic carbon could be removed absolutely. The best condition of acid fumigation method was that the samples treated for 12 h to 18 h, and the appropriate reaction time should be according to the concentration of the sedimentary inorganic carbon. At the best condition of the two methods, the standard deviation of the data could meet the requirements of IRMS, which proved that the two methods were suitable for sedimentary organic carbon measurement.