Stable carbon isotope ratio (13C/12C) has been widely used in geochemistry, paleoclimatology and paleoceanography researches. It is well known that C3 and C4 plants have different isotope signatures. The reason for the difference can be attributed to difference in reaction rates differs caused by mass difference of 13C and 12C containing molecules. The stable carbon isotope ratios of organic sediments have been used to study geochemical origin and correlation between different area. Generally, stable isotope analysis of carbon is performed by burning an aliquot of material and analyzing the generated CO2 gas by using specially designed sector mass spectrometry. Quantitative isotope ratio data can be obtained by using this method. However, the method is limited to obtain the ratio at the molecular level. Therefore, in this study, ultra-high resolution mass spectrometry has been evaluated for feasibility of molecular level 13carbon isotope analysis. For the evaluation of crude oils, they were analyzed by (+) atmospheric pressure photo ionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). And For the evaluation of humic acids, they were analyzed by (-) electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In crude oils data, isotope ratio of sulfur class compounds were evaluated by using the equation, as well as humic acid data isotope ratio of oxygen compounds were evaluated by using same method. The obtained data were compared between organic sediments originated from different locations. The isotope ratio calculated from FT-ICR MS data were compared with the bulk ratio obtained with Elemental Analyzer–Isotope ratio mass spectrometry (EA-IRMS).