Three different plant communities typical of the forest region of the Yanhe River watershed in the Loess Plateau were selected as subjects in study to explore effects of vegetation community on content and composition of organic carbon and activities of soil enzymes in soil aggregates, and relationships between organic carbon and enzyme activities, Results show that in all the three soils, regardless of vegetation community, soil aggregates in the 0~10 cm soil layer were higher than those in the 10~20 cm layer in content of organic carbon regarless of fraction and in activity of all soil enzymes, except for ployphenol oxidase, which was higher in the 10~20 cm soil layer than in the 0~10 cm soil layer under the Quercus liaotungensis community; that in terms of soil organic carbon content in soil aggregates the vegetation communities displayed an order of Quercus liaotungensis community > Robinia pseudoacacia community > Sophora viciifolia community, while the three vegetation communities did not show any consistent trend in soil enzyme activity, and the content of organic carbon and the activity of oil enzymes increased with increasing particle size of soil aggregates or increased first and then declined afterwards; significant positive relationships were observed of the activities of sucrase, cellulase and β-D-glucosidase with soil organic carbon of all forms, but no such relationships were of the activities of ployphenol oxidase and peroxidase with soil organic carbon; that in the soils under the Quercus liaotungensis and Shrub Sophora communities, the fractions of soil aggregates displayed an order of |<0.25 mm| > |2~0.25 mm| > |5~2 mm| > |>5 mm| in activities of sucrase, cellulase and β-D-glucosidase, but the fraction of 2~0.25 mm aggregates was the highest in activities of loyphenol oxidase and Peroxidase in both of the soils and in the soil under Black Locust community the fraction was the highest in activities of all the soil enzymes; and that higher activity of soil β-D-glucosidase contributed to the increase of soil organic carbon of all the forms, that of soil sucrase and β-D-glucosidase did to the increase of soil active organic carbon, and that of soil Ployphenol oxidase did to the accumulation of humus carbon.