Obtaining certified seed material requires a number of physical actions which in turn call for the knowledge of rules governing separation processes. They are based on the recognition of some physical and mechanical differences in properties between various components of seed mixtures. This kind of knowledge is further required when designing and building various sub-assemblies of machinery and equipment used in improving seed material, in operating effectively seed cleaners and mechanical seed sorters as well as other machinery used in seed processing. Both contemporary and older designs of separators utilise the experience of practitioners rather than the theoretical concepts rooted in deep knowledge of agrophysics of seeds. In view of the above, there is a necessity of a detailed analysis of separation-related properties of the Pedunculate Oak acorns, including the features not yet used in forestry, but which should be considered when designing future universal separators. Mechanical separation of seeds requires knowledge about their fundamental planimetric parameters like linear dimensions, cross-section areas and cross-section circumferences. Measurements of the mentioned parameters are quite simple with the help of computer image analysis. Seed images can be obtained, among others, from the digital camera. The aim of this work was an analysis of size and shape of the Pedunculate Oak acorns (Quercus robur L.) determined by shape coefficients, in correlation with their viability. A classification of seeds was adopted dividing them into three measurement fractions, based on the development of the embryo and the predicted seed germination capacity. The results of the studies showed that geometric properties of the acorns cannot be regarded as separation properties, so the separation of the seeds cannot be performed by basing the process on the size of seeds. In the course of the study it was also noted that the traditional method of drying acorns in order to prepare them for storage failed to assure uniform final moisture content. The most valuable seeds, vital ones with large seed embryos, have significantly higher moisture content than other seeds. This is perhaps the reason behind a drop in the germination capacity of seeds during storage.