Accurate assessment of soil organic carbon storage based on the database established on the basis of the attribute data of soil profiles is the basis of the research on global carbon cycling and improvement of soil fertility for agriculture. However, it is still unclear how source of soil profile data and scale of mapping affects assessment of soil organic carbon storage. In this study, a total of 3.93×10⁶ hm² of upland in the 29 counties (or cities) of North Jiangsu was cited as a case for study. Systematic analysis was performed of how the four sources of soil profile data, namely, “Soils of County”, “Soils of Prefecture”, “Soils of Province” and “Soils of China”, and the six scales, i.e. 1:50 000, 1:250 000, 1:500 000, 1:1 000 000, 1:4 000 000 and 1:10 000 000, used in the 24 soil databases established for the four soil journals, affected assessment of soil organic carbon. Results show that the soil organic carbon density (SOCD) and storage (SOCS) in the top layer (0~20 cm) of the uplands in the region in the 1:50 000, 1:250 000, 1:500 000, 1:1 000 000, 1:4 000 000 and 1:10 000 000 scaled databases was estimated to be 1.56 kg m^-2 and 61.20 Tg, 1.53 kg m^-2 and 61.32 Tg, 1.51 kg m^-2 and 61.22 Tg, 1.44 kg m^-2 and 55.19 Tg, 1.60 kg m^-2 and 65.08 Tg, 1.59 kg m^-2 and 63.11 Tg, respectively, based on 983 upland soil profiles in the “Soils of County”, 1.63 kg m^-2 and 63.92 Tg, 1.71 kg m^-2 and 68.78 Tg, 1.64 kg m^-2 and 66.37 Tg, 1.62 kg m^-2 and 62.06 Tg, 1.70 kg m^-2 and 69.25 Tg, 1.72 kg m^-2 and 68.24 Tg, respectively, based on the 209 upland soil profiles in the “Soils of Prefecture”, 1.27 kg m^-2 and 49.88 Tg, 1.25 kg m^-2 and 50.06 Tg, 1.72 kg m^-2 and 69.64 Tg, 1.43 kg m^-2 and 54.84 Tg, 1.40 kg m^-2and 56.99 Tg, 1.52 kg m^-2 and 60.18 Tg, respectively, based on 64 upland soil profiles in the “Soils of Province”, and 1.74 kg m^-2 and 68.31 Tg, 1.70 kg m^-2 and 68.08 Tg, 1.81 kg m^-2 and73.52 Tg, 1.75 kg m^-2 and 66.78 Tg, 1.75 kg m^-2 and 71.33 Tg, 1.19 kg m^-2 and 47.21 Tg, respectively, based on 21 upland soil profiles in the “Soils of China”. Compared with the most detailed 1:50 000 soil database based on 983 upland soil profiles containing 17 024 polygons. the other five databases varied from 1.94% to 23.53% and from 0.02% to 22.86%, respectively, in relative deviation of the assessment of SOCD and SOCS. T test shows that extremely significant differences existed between the assessment based on the 1:50 000 database of “Soils of County” and the assessments based on the databases of other scales (p＜0.001), indicating that it is essential for scientists to use soil data from proper sources and of proper mapping scales when trying to assess SOCS of the country or a region in future.