Biological soil crusts are widely distributed in the desert as an important biological factor to stabi-lize the sand dunes and promote restoration of sandy ecosystem. Landsat remote sensing images of Mu Us Desert in 1989

2002 and 2006 were used to extract spatial distribution of biological soil crusts and land de-sertification based on the biological soil crust index and NDVI threshold. Furthermore

the relationship be-tween biological soil crusts and land desertification was discussed. The results show that the areas covered by biological crusts accounted for 54.77%

55.72% and 64.29% of the total area in the three study years

re-spectively

indicating biological soil crusts in the study area increased continuously. In addition

the connec-tivity among crust patches was enhanced

and the crust stability was further strengthened. In contrast

the degree of land desertification was gradually weakened during the study period

as the composite index of land desertification dropped to 2.65 in 2006 from 3.24 in 1989. Biological soil crusts distributed most widely(over 70%) in the lands experienced moderate and severe desertification. However

the area of biological soil crusts continued to decline in extremely severely desertified lands

accounting for 19. 40%

5. 76% and 2.80 % of the total area of the extremely severely desertified land in the three study years

respectively. The number of biological soil crusts was increasing in extremely severe desertification land

indicated by the ratio of 19.40%

33.18% and 45.21% in the three study years

respectively.