In order to provide a scientific basis for biodiversity protection on the Ordos Plateau, we compared plant community diversity in 1999 and 2000 with that in 1986 (Li, 1990). The results indicated that the 23 major types of plant communities showed significant differences in Simpson index, Shannon-Wiener index, and coverage, but similar richness. Higher diversity and higher coverage occurred in the typical steppe in the middle-eastern sector of the plateau, while higher diversity but lower coverage was found in the desert-steppe and steppe-desert in the west, and lower diversity but higher coverage was found in the communities of the Maowusu sandland. From 1986 to 2000, the biodiversity and coverage of the communities had changed ob- viously. The biodiversity of typical steppe, desert-steppe and sandland vegetation showed a decreasing trend, whereas coverage of typical steppe and steppe-desert increased, and the coverage of the desert-steppe de- creased. We recommend that great attention should be paid to the ecological conservation of the desert-steppe as well as to species diversity of sandland vegetation and steppe desert.