The present study applies supercritical water oxidation (SCWO) as a pretreatment method for the stable carbon isotope ratio analysis of rice. In this study, three kinds of polished rice with different locations of production were treated by SCWO using a batch-type reactor. At a temperature of 500 degrees C, pressure of 25 MPa, and reaction time of 120 min with an excessive amount of oxygen, more than 99% of the rice-derived organic carbon was converted into carbon dioxide without generating any other C-containing gases. Utilizing TiO2 as a catalyst, 99.5% of rice-derived organic carbon was selectively converted into CO2 within 15 min. In each case, the stable carbon isotope ratio of generated CO2 was successfully obtained using isotope ratio mass spectrometry. The delta C-13 value of CO2 from the SCWO treatment of rice was compared with that of CO2 from the catalytic combustion of rice.