Application of secondary products of oilseed crops processing, which due to high nutritional and biological value, can be enriching ingredients during production of functional food products, is an important area of research and improvement of food technology. The paper presents the results of study of physical and chemical, fatty acid and vitamin and mineral composition, as well as nutritional value of domestic flaxseed fiber samples in Belarus. Based on data obtained, it was determined that flaxseed fiber can be used for production of functional food concentrates with the purpose to enrich them with dietary fibers, polyunsaturated fatty acids and protein. When choosing food concentrates for enrichment with these nutrients, current trends of food industry development focused on production of high nutritional value products of in bulk consumption were considered, including the level of physiologically active ingredients, instant food, with long shelf life, etc. Assortment of new types of food concentrates with flaxseed fiber has been developed. Mathematical simulation methods helped to determine rational dosages of enrichment ingredient, experimental batches of products were produced, their nutritional value, quality and safety indicators were studied. The data obtained can be used for design of new types of enriched and specialized food products.