H2/CO2 reduction and CH3COOH fermentation are the two major pathways of methanogenesis in rice fields. Carbon isotope tracer technique, the use of specific inhibitors to block methanogenesis and stable carbon isotope ratio measurement has been used to quantify the partitioning of methanogenic pathways. The paper summarized the three approaches and the corresponding results. The research emphases in the future are to investigate the methanogenic pathways in rice fields in China, to comparatively analyze the three approaches and find out the cause of the difference in the results, and to investigate carbon isotope fractionation factors (a(CO2/CH4) and e(ac/CH4)) and stable carbon isotope compositions of CH4 (δ13CH4 and δ13CH4(CO2/H2)).