Abstract: In 2002 - 2004 the population of the dolichoderine ant Liometopum microcephalum (Panzer, 1798) in South Moravia (Czech Republic), at the northwestern boundary of the species' range, was surveyed in terms of distribution, population size (number of colonies) and habitat requirements. At present the northern-most colonies in South Moravia occur at the Křivé jezero National Nature Reserve on the Dyje river and in the Skařiny Nature Reserve on the Morava River. In total, 850 colonies were recorded and the characteristics of their nest trees analysed. About one half of the nest trees were found within forest stands and 94 percent of all nest trees were oaks. Most sites with colonies are located within the active or historic floodplains. Due to the river regulation between 1970 and 1989 (including the construction of reservoirs on the Dyje) and due to present forest and park management this population has retreated to the south and is to be considered threatened despite its considerable size.