Resource efficiency plays an important role in implementation of the Europe 2020 Strategy, being a roadmap for sustainable development. Because of limited fossil resources, sustainable development is not achievable without the use of renewable resources whenever possible. Renewable natural resources offer a vast source for development of effective solutions in energetics, building, automotive and other sectors of national economy. Of particular interest to the international community is purposeful use of natural waste products. In this context, the current research is focused on the evaluation of the suitability of agricultural waste products, such as oat and spelt husks (OH and SH, respectively), for reinforcing of polypropylene, thus trying to find economically and technologically viable alternatives to wood flour (WF) containing polymer composites. By considering that aspect ratio plays an important role in determining reinforcement efficiency of the filler, especial attention has been paid to elaboration of mechanical pretreatment procedures of OH and SH, by considering technological parameters such as grinding speed and time. Beyond mechanical milling/sieving protocols, suitability of the lab-scale steam explosion processing has been also evaluated. Steam explosion treatment of natural fibers is known to ensure increased cellulose content [1-3], as well as higher surface area [3], being important indicators for increased reinforcing efficiency of the lignocellulosic filler in the polymer matrix.