The present work was carried out as a part of the activity of Global Environment Facility Sponsored Soil Organic Carbon Project. Century C model was evaluated using selected sites under Long-Term Fertilizer Trials (LTFT) in the Indo-Gangetic Plains (IGP), India. All the LTFTs were undertaken to determine optimum fertilizer rates for obtaining maximum yields of rice and wheat, as rice and wheat are the major crops in the study area. Model simulations were evaluated against the measured and the modeled data. The best correlation between measured and modelled SOC data was observed with high levels of N fertilizer in combination with high FYM (15 t/ha/yr). Model simulation of the control treatment (no fertilizer and no FYM) corresponded very closely with measured SOC values. The study indicates that Century model can predict treatment effects in LTFTs carried out in India. An attempt was also made to compare the SOC stocks predicted from the GEFSOC Modelling System© with stocks generated using a mapping approach based on soil survey data. The GEFSOC Modelling System© predicts an estimated SOC stock for the IGP, India of 1.64, 1.71 and 1.64 Pg (0-20 cm depth)for 1990, 2000 and 2030 respectively, whereas mapping-approach-based soil survey data showed 0.66 and 0.88 Pg SOC stock (0-20 cm depth)for 1980 and 2000 respectively. This variation may be due to crop input data (crop management) inflating the modelled SOC stock. The trend of overall change in the modelled SOC stock estimates shows that the IGP, India may have reached an equilibrium following 30-40 years of the Green Revolution. Similarly, the trend of overall change in C stock assessed from soil the survey data indicates that the soils of IGP, India may store a projected 1.1 Pg of C in 2030.