One of the post-production wastes generated by industries acquiring herbal materials are fine-grained wastes produced during the packing of herbs. The company Herbapol Bialystok S.A. produces approx 30 tons per year of such wastes, and the most frequent way of their utilisation is their applying as an addition to farm fodders. The paper presents the results of investigations of water activity (as the critical parameter of the control of quality) in fine-grained postproduction wastes of lemon balm (Melissa officinalis) in dependence on the moisture and the particles size of the wastes, and of the morphology analysis of lemon balm particles in relation to the shape coefficients, performed with the use of stereological methods and computer image analysis. The morphology analysis of lemon balm particles comprised the following parameters:the fraction of particle area (convexity), the elongation factor, and the shape factor. The results of the investigations show that an increase of the wastes moisture from 7.60 to 15.33% causes the growth of water activity from the value of 0.341 to the level of 0.798. Increase of the particles size of the wastes from d < 0.063 mm to particle size of 0.25 mm < d < 0.5 mm (at moisture of 10.33%) causes the growth of water activity from the value of 0.562 to 0.598. To prevent the development of mould in lemon balm wastes, they should be kept in conditions guaranteeing the maintenance of moisture below 10%. The influence of  moisture and particle size of lemon balm wastes on the water activity can be described with a logarithmic function equation. Conducted microscopic observations and their analysis showed that most of the particles of lemon balm wastes (except the largest particles, with diameter d>0.5 mm) are characterised by shapes approximate to the sphere.