Biological soil crusts (BSCs) play an important role in fixation of sand dunes and maintenance of soil biota in arid desert ecosystems. Soil enzyme activities could be used as significant bioindicators of extent of soil restoration and important biological indices in evaluating ecological restoration and health in sandy areas. However, so far little has been reported on relationship between BSCs and soil enzyme activities. To understand how BSCs affect soil enzyme activities, sand dune soil under BSCs in the artificially revegetated areas at the southeastern edge of the Tengger Desert, China was taken as object of this study. Four sample lots different in sand-fixing history (57, 49, 32 and 22 a, respectively) were set for soil sampling, and a tract of mobile sand dunes (0 a) and a tract of natural vegetation land (>100 a) in Hongweiof Shapotou were set as control. Results show that cyanobacteria-lichen and moss crusts could significantly increase activities of soil alkaline phosphatase, protease and cellulase in the artificial revegetation sand fixing areas (p < 0.05). Type of crust significantly affected soil enzyme activities. The effects of moss crusts, typical of the late stage development of BSCs on activities of soil alkaline phosphatase, protease and cellulase were much higher than cyanobacteria-lichen crusts, typical of the early stage development of BSCs（p < 0.05). Sand-fixing history also significantly affected activities of the soil enzymes, displaying a positive linear relationship with activities of the soil enzymes（p < 0.05). BSCs significantly enhanced activities of the soil enzymes in the 0~20 cm soil layer（p < 0.05) and the effects weakened with increasing soil depth. Moreover, activities of the soil enzymes under the crusts varied with the season, following an order of summer > autumn > spring and winter. Therefore, apparently, the presence and succession of BSCs increases activities of the soil enzymes. The findings indicate that BSCs are beneficial to restoration of soil and corresponding ecological systems in the artificially revegetated desert areas at the southeastern edge of the Tengger Desert.