In the future, composite materials based on plant fibres will have increasing importance in our life. They are light, recyclable, environment friendly. Plant fibres can substitute the artificial fibres in many industrial products even if manmade fibres at present still perform better. Nevertheless, appropriate dry-mechanical treatment of raw material can improve plant fibre characteristics; subsequent chemical treatments are able to induce fibre modifications that increase their resistance when utilised in composite products. This paper will describe the hemp, flax and kenaf dry-mechanical preparation system. results on treatment yield and characteristics of different fractions will be given for each species. Afterwards. the composites preparation system will be described and results of fibre behaviour in composite products will be illustrated and discussed.