In the dust of organic plant origin the presence of micro organisms, particularly moulds and endotoxins, is recorded to have harmful effects on the human body and cause many diseases. The microbiological quality of the processed plants is largely dependent on the fragment of the plant used as raw material, since the microbial contaminants are the result of different contacts of each particular part of the plant with the external environment during cultivation and further processing. Organic dust present in the plant raw material may be varied not only in terms of microbial contamination, but also regarding the size of particles thereof. In the presented study an attempt was made to identify fungi found in the organic dust sampled in an herb processing plant located in eastern Poland. The concentrations of PM10 and PM 1.0 were determined within two production lines, and these values were then referred to the existing regulations. The mean concentration of PM10 significantly exceeded the alert level.