AbstractPhyllanthus emblica (Euphorbiaceae) is one of the dominant species distributed in dry-hot valleys of southwestern China. Besides its function in ecology, environment and reforestation, it is also an important medicinal plant. We studied the genetic diversity in four populations of P. emblica sampled from dry-hot valleys of Yunnan using ISSR (inter-simple sequence repeats) markers. Based on 12 primers, 135 clear and reproducible DNA fragments were generated, of which 115 were polymorphic, accounting for 85.19%. The coefficient of genetic differentiation (G_ST) equaled 0.1222. Such a high level of genetic diversity and low level of population genetic differentiation might result from the breeding system of this species. There was a lack of significant association between genetic and geographical distances (r=0.19798, P=0.6513>0.05) among P. emblica populations. The results suggest some important recommendations about sampling meth-ods to be used in ecological reforestation of dry-hot river valleys.