Humanity today is experiencing a dramatic shift to urban living. Land coverage changes to build cities and to support the demands of urban populations themselves drive other types of environmental change. Urban development is associated with physical changes to the landscape, such as increased impervious surface area and the replacement of natural vegetation with lawns, which can positively or negatively alter soil organic carbon (SOC) stocks. However, little is known about the characteristics and potential drivers of SOC variability in urban areas. Urban plus rural residential lands are one of the largest land use zones in a city and its suburban area. Therefore, one would expect changes in SOC stocks with the residential land use changes such as urbanization. In this study, residential land information was extracted from high resolution imagery of Nantai Island in the Cangshan District, Fuzhou City, then 50 soil sampling plots were randomly selected from residential sites based on a 30m×30m sampling grid covering the island. Variability of soil organic carbon density (SOCD) in residential sites and its affecting factors were analyzed in this rapidly urbanizing area. The results indicated that because of an intense interference by human activities, soil in urban residential areas has a strong spatial heterogeneity. Average SOCD was 33.814t/hm², with a variation coefficient of 72.8%. The SOCD in the surface layer (0-20cm) of the rural residential area was 72% higher than that of urban residential land, which indicated that SOC stocks declined with the situ urbanization in the rural area. However, both SOC content and density in the 10-15 year group of housing developments were significantly higher than those in the group with housing developments less than 10 years old, although there was no significant difference between the 0-5 and 5-10year housing developments. The recovery of urban residential SOC stock, compared to rural residential, requires longer accumulation time. A composite index developed in this study for urban residential green space management quality, which combined humidity, heat, green coverage ratio, and property management fees by a principal component analysis, showed a significant linear positive correlation with SOC content and density, and negative correlation with bulk density. Therefore, residential green space management was another factor affecting SOCD variation in a rapidly urbanizing area. Although the conversion of rural residential into urban residential land will lead to SOCD declines because of the reduction of exogenous organic material input, the living environment has been improved, and the management of green space also contributes to the improvement of urban soil quality.