The aim of this diploma thesis was to determine the frequency and occurrence of invasive alien plant species along the Ledava River. Research was carried out in the summer of 2016. Twenty locations along the Ledava River were surveyed. The first location was close to the Austrian border, while the last location was at the border with Hungary. At each location, the condition of the river and the presence and abundance of invasive alien plant species were assessed using a questionnaire. Seven invasive alien species were recorded. The presence, abundance, phenological phase, frequency, cover and vitality of these invasive alien species were assessed. Data analysis revealed that the two most frequent species were Solidago gigantea and Impatiens glandulifera. The results are presented in the graphic form.