【Objective】Soil organic carbon (SOC) is an important part of the terrestrial carbon pool. Owing to its critical role in the global carbon cycle and its heavy storage in the terrestrial ecosystem, any slight change in the SOC pool would sure create certain influence on global climate. So, in order to simulate the global carbon cycle and design agricultural management measures, it is essential to estimate soil organic carbon storage (SOCS) accurately. Because of the spatial heterogeneity of soil properties, the study on SOC estimation on a regional scale may help improve accuracy of the estimation of SOC on the global scale, and moreover provide eco-environmental protection, regional decision-making and agricultural sustainable development with data support.【Method】In this study, based on the soil database of Fujian Province, and soil maps of the province, different in scale (1:50 000, 1:200 000, 1:500 000, 1:1 000 000, 1:4 000 000 and 1:10 000 000), SOCS were estimated for analysis of spatial distribution of SOC in the surface soil layer (0～20 cm) and soil profile (0～100 cm). The PKB method, i.e, pedological knowledge based method, was used to relate soil spatial data to soil attributes. As affected by the scale of a soil map, the number of soil patches decreased from 247 969 to 46 408, 15 282, 6 343, 440 and 345, with declining mapping scale and 3 082, 3 082, 2 718, 2 547, 1 000 and 890 soil profiles were made available for collection of soil physico-chemical properties, respectively. No doubt, the change in scale of soil mapping would sure bring about uncertainties in estimation of SOCS.【Result】Results show that based on the six soil maps different in mapping scale SOC in the surface soil layer (0~20cm) was estimated at 552, 637, 573, 573, 614 and 549 Tg C and in the soil profile (0~100 cm) at 1 396, 1 502, 1 321, 1 395, 1 508 and 1 532 Tg, respectively.. Estimation of SOC in skeleton soil, among all the types of soils, was most affected by mapping scale, with relative deviation in the surface soil layer and soil profile being 88.75×104% and 81.96 ×104%, respectively. However, the estimation of SOC density in the surface soil layer of red soil, the largest in land area, was, the lowest in relative deviation, being 4.28%, based on the soil map 1:1 000 000 in scale, while the estimation of SOC density in the soil profile was the lowest in relative deviation, being only 1.53%, based on the soil map, 1:500 000 in scale. The estimation of SOCS in Xiamen and Fuzhou, in terms of administrative region, were both affected by mapping scale, with relative deviation being 26.44% for topsoils and 27.97% for soil profiles, respectively. Relative deviations of the estimations of SOC density in the surface soil layer and profile in all the cities, except Xiamen, based on the soil map 1:500 000 in scale, were the lowest.【Conclusion】In general, regarding Fujian Province as a whole, the estimation of SOC density and storage in the surface soil layer and profile based on the soil map 1:1 000 000 in scale deviated the least from the currently available most detailed large-region data, 1:50 000 in scale, being 0.67% and 0.82% respectively, while that based on the soil map 1: 200 000 in scale did more, reaching 15.57% and 15.34% respectively. Estimation of SOCS in the surface soil layer and profile of Skeleton soil, among all the types of soils, was the most affected with relative deviation, reaching up to 88.75×104 % and 81.96 ×104%, respectively. The estimation of SOC density in the surface soil layer of red soil was the lowest in relative deviation, reaching 4.28% based on the soil map 1:1 000 000 scale and that in the soil profile of the red soil was, reaching 1.53% based on the soil map 1:500 000 in scale. The influence of mapping scale is also significant for Xiamen and Fuzhou. The relative deviation of the estimation of SOCS in the surface soil layer of Xiamen was 26.44%, and in the soil profile of Fuzhou was 27.97%. The relative deviations of the estimations of SOC density in both the surface soil layer and profile in all the cities, except Xiamen based on the soil map 1:500 000 in scale, were the lowest. All the findings in the study demonstrate that mapping scales does have certain influences on estimation of SOCS in the soils of the same area. In the case that administrators of an area do not have any accurate soil databases, it is advisable for them to estimate SOCS in their region and design agricultural management measures based on the soil map 1:500 000 in mapping scale.