Abstract: Introduced a new method to prepare organic carbon isotopic sample for mass spectrometric analysis. The sample consisting of organic compounds is combusted in static oxidation condition at high temperature to produce CO₂ and H₂O, then followed by separation and conversion. The δ¹³C value of the CO₂ is measured with a mass spectrometer. A combustion temperature above 900℃ is used to guarantee complete oxidation of both reactive and resistant organic materials. This technique has the advantage of accuracy, convenience and safety. It can be used in most isotopic laboratories.