Through indoor analysis and incubation of soil samples collected from fields in the Yangtze Delta region, differences in soil organic carbon mineralization and enzyme activities between soils different in duration of vegetable plantation were observed. Findings showed that NO₃^--N content in the soils increased significantly with the duration because of application of large amounts of chemical fertilizer or/and organic manure. Mineralization rate of soil organic carbon, during the early period of incubation, decreased with the increase in duration. Activities of soil urease and invertase also decreased with the increase in duration, while soil phosphatase increased owing to phosphorus accumulation in the soil from application of large amounts of phosphate fertilizer. Soil phosphatase and invertase activities were significantly correlated to soil organic carbon and total nitrogen content. Soil enzyme activity varied obviously with duration of vegetable plantation and could be cited as a sensitive indicator of changes in soil quality.