The application relates to a process for producing fibrous material with antimicrobial properties, wherein in the first step coniferous resin acid composition is emulsified into aqueous solution with emulsifier and wetting agent, and in the second step thus formed emulsion is transferred into fibrous material by impregnation. Further, the application relates to an aqueous antimicrobial composition for use as a water-soluble concentrate in the treatment of fibrous materials, and to a fibrous material with antimicrobial properties, and to its use in e.g. fabrics, fur, leather, clothes, canvas, tissues, plastics, webs, accessories, packaging materials, wallpapers, food-related products, household products, footwear, construction materials, insulating materials and medical products.