This study has been conducted in order to examine and investigate the use of a natural material. While synthetic fibers are limited with regard to resources needed for their production, natural fibers are always renewable and degradable, and their required life-time and strength are comparable with those of synthetic fibers. In the present study, the application fields of natural fibers, technical properties of natural fibers, types of natural fibers, fiber treatment methods, chemical structures of natural fibers, natural fiber compatible matrix materials, limitations and renewability of natural fibers are analysed. Flax fiber polymer matrix (with nano additives) composites were fabricated using fibers with treated and untreated surface. Composite coupons were tested by tension till failure. Mechanical behaviour of materials with treated and untreated fibers were compared and analysed.