The effects of Spartina alterniflora invasion on soil labile organic carbon (LOC) and enzyme (urease, catalase, alkaline phosphatase, invertase) activities were investigated in the Yanghe estuary wetland of Jiaozhou Bay. Soil samples were collected at 0-60 cm depths in different invasion years (0, 1, 5, and 8). The responses of LOC and soil enzyme activity to Spartina alterniflora invasion, and the relationship between them, were assessed. The results showed that Spartina alterniflora invasion significantly increased LOC contents of the surface layer in comparison to that of the mudflat (P < 0.05), and the soil LOC contents increased significantly with the increase of invasion time. Meanwhile, Spartina alterniflora invasion also changed the rule of vertical dynamics of LOC contents. Sample plot LOC first showed an increasing trend, and then decreased along the soil profile except that LOC contents of the two plots increased along the entire soil profile. Spartina alterniflora invasion increased the soil enzyme activities, but it did not change their distribution rule, as they decreased with increasing soil depth. The variation trend of 4 types of enzyme activities changed with the increase of Spartina alterniflora invasion time. The catalase and invertase activities first showed a dramatic increase and then a gradual decrease, but alkaline phosphatase and urease activities gradually increased with the increase in invasion time. Pearson correlation analysis showed that soil labile organic carbon was significantly negatively correlated with enzyme activity, and the correlation decreased with the increase of invasion time; it disappeared after 8 years.