Between 1996 and 1998, we researched on eight study plots in Sedliská Nature Reserve and its vicinity qualitative and quantitative structure of lepidopterocenoses based on the degree of the impact of anthropogenic factors. The results show that a total of 76 species from the superfamilies Zygaenoidea and Papilionoidea were recorded on the study area. During the whole research period, including also inventory research in the period 1974–1976, 109 lepidopterous species were found in Sedliská Nature Reserve and its vicinity. In the period between the two researches 33 species probably disappeared and 10 new species appeared. The highest number of species were found on the study plot with the most well-preserved original forest-steppe character and least affected by human activities. The least species were recorded on the plot with northwestern exposure most affected by human impact. Pieris rapae (Linnaeus, 1758), P. napi (Linnaeus, 1758) and Zygaena carniolica (Scopoli, 1763) achieved the highest dominance. Pieris rapae and P. napi showed high dominance on the plot affected by the use of agrochemicals and on the plot of ruderal plant communities. Our results emphasize the importance of the study area and show that the Sedliská Nature Reserve is one of the rare xerothermic localities of Slovakia. There is no doubt that this reserve deserves protection and further attention.