Abstract: The aged leaves of wild Medicago rutenica in 32 populations were observed in Inner Mongolia using paraffin wax embedded sections to analyse and evaluate drought resistance. Optical microscopy was used to measure the anatomical structure of drought-related parameters including the thicknesses of the upper and lower cuticles, leaf, palisade and spongy tissues, the diameter of the vascular bundles, the ratio of palisade to spongy tissue, the tightness of leaf palisade tissue structure and the looseness of leaf sponge tissue structure. Nine indexes differed significantly. There were significant correlations between the thicknesses of the upper and lower cuticles, leaf, palisade and spongy tissues and drought resistance. The eigen value of the third principle component was 1.621 and accumulative rate was 86.67%. The first three principle factors generalized the main information of 9 characters. The 32 populations were divided into 5 groups by the UPGMA method. The membership function to evaluate drought resistance showed that No.16 and 27 had strong drought-resistant while No.22 was weak.