Authors' contribution Wkład autorów: A. Study design/planning zaplanowanie badań B. Data collection/entry zebranie danych C. Data analysis/statistics dane-analiza i statystyki D. Data interpretation interpretacja danych E. Preparation of manuscript przygotowanie artykułu F. literature analysis/search wyszukiwanie i analiza literatury G. Funds collection zebranie funduszy Summary Background. Herbs are used in both the food and pharmaceutical industry. The quality of products received from herbal raw materials depends primarily on the microbiological purity of herbs. The presence of germs in food products contributes to developing alimentary infections and to the contamination of food with mycotoxins. Decontamination with ultraviolet UV-C rays is a proven way to enhance the microbiological purity of food products as radiation directly affects the structure of the nucleic acid of living organisms and destroys them without selective biocidal activity. The aim of the study was to determine the microbiological purity of selected species of herbs and assess the possibility of using UV-C radiation to increase it. Material and methods. The scope of work included the separation of three dimensional fractions of dried herbs such as thyme, medical cistus and stinging nettle, and then subjecting them to UV-C light and determining the total number of germs in the herbs with respect to the control sample, which consisted of untreated herbs. Results. The tested herbs were characterised by diversified microbiological purity, depending on the species and a type of size fraction. Sterilisation of herbs with UV-C radiations allowed for increasing their microbiological purity as compared to the control sample, in the case of the fraction with the largest particle size by about 37%-thyme, 73%-cistus and 30%-nettle. Conclusions. The use of UV-C radiation allowed for considerable reduction of the number of germs found in the examined herbs.