Abstract: Bioenergy is considered as the most promising energy source under the energy crisis in the 21st century. Miscanthus sinensis is a very good bioenergy candidate because of its high biomass, good burning quality, environmental tolerance, and tolerance of marginal land for growth. To investigate the phenotypic variation and relationships of different wild M. sinensis populations collected from southwestern China, a project was carried out to study nine botanical characteristics and yield characters of 37 wild M. sinensis populations. There were significant differences (P<0.01) between populations in all characteristics studied. Abundant morphological variation was detected in accessions of M. sinensis and their coefficients of variation were ranked as follows: dry weight of individual plant (46.89%)＞fresh weight of individual plant (46.34%)＞tiller numbers (44.08%)＞flag leaf length (33.99%)＞flag leaf width (27.40%)＞leaf width (19.59%)＞internode number (18.76%)＞internode length (18.49%)＞stem diameter (17.89%)＞plant height (14.64%)＞leaf length (12.83%). Phenotypic characteristics of M. sinensis were also significantly correlated. Those accessions with long and wide leaves were tall plants with longer and wider flag leaves, wider stems, but fewer tillers, and vice versa. In addition, the weight of individual plants was significantly correlated with tiller numbers, plant height, and leaf length which suggests that these characteristics should be improved and evaluated for future applications. Principal component analysis based on nine morphological characteristics showed that four principal components reflected most of the plant phenotypic characteristics. Thirty-seven populations were divided into 3 categories based on Euclidean distance clustering analysis which included tall plants with long and narrow leaves, tall plants with long and wide leaves, as well as short plants with short and narrow leaves.