To comprehensively understand the natural succession of plant communities in the Alxa Desert, we studied the seasonal changes for RNA, DNA and protein contents, and the ratios of RNA/DNA ratio and RNA/protein ratio of constructive species, and compared these differences at different successional stages. The study site, located at 38°24'59″N, 105°43'31″E, is 8 km away from the Bayinhaote town of Alxa Left Banner of Inner Mongolia Autonomous Region, China. The succession series of plant community in this study area are as follows: In the early successional stage, community is dominated by Artemisia sphaerocephalla; at mid-successional stage, the plant communities are dominated by A. ordosica and A. frigida; and at late-successional stage, it developed into a relatively stable Oxytropis aciphylla community. In A. ordosica + A. frigida community, the A. ordosica was furthermore replaced by A. frigida. As to the cause for plant community succession, the difference of plant relative growth rate for the replaced species and/or substitute species is usually considered to be one of the major factors. Theoretically, plant RNA/DNA ratio and RNA/protein ratio may be related to plant relative growth rate, so we hypothesize that the difference to the RNA/DNA ratio or RNA/protein ratio may take on among the constructive species in the progressive successional series or between the replaced species and the substitute species in the successional community. In the present study, we collected the fresh and tender leaves of A. sphaerocephalla, A. ordosica, A. frigida and O. aciphylla at 9:00, 12:00, 15:00 and 18:00 on the May 26, July 26 and September 26 in 2012, respectively, and analyzed the seasonal changes of their RNA, DNA, protein, RNA/DNA ratio and RNA/protein ratio. The results showed that the lowest DNA content was in May for all four plants, and the highest value of A. sphaerocephalla and O. aciphylla appeared in July, while for the A. ordosica and A. frigida, it increased gradually from May to September. For leaf RNA content, the highest value of A. ordosica and A. frigida was in July, while for A. sphaerocephalla, the highest and lowest values occurred in May and July, respectively, and the RNA content of O. aciphylla increased gradually from May to September. However, the same changes of leaf protein content were found for four plants, the lowest and highest values appeared in July and September, respectively. For leaf RNA/DNA ratios, the lowest value for A. sphaerocephalla and O. aciphylla was in July, while the highest value presented in July for A. ordosica and A. frigida. Moreover, the mean RNA/DNA ratio during the growing season decreased gradually with progressive succession process. For leaf RNA/protein ratios, the highest value was in July for four plants. The mean RNA/protein ratio of the substitute species-A. frigida was higher than that of the replaced species-A. ordosica at the mid-successional stage of A. ordosica + A. frigida community. The results suggest that the leaf RNA/DNA ratios and RNA/protein ratios had obvious seasonal changes from early successional stage to late successional stage.