A `bioactive` composition that has one or more oligogalacturonans ((1.fwdarw.4)-.alpha.-D-galacturonan) or any other oligosaccharides (oligoguluronans) that may present an `egg box` conformation, this conformation being further stabilized by one or more polycationic saccharide(s), preferably either a chitosan oligosaccharide or a chitosan polysaccharide. A method prepares this composition and it is used, in medical, pharmaceutical, agricultural, nutraceutical, food, feed, textile, cosmetic, industrial and/or environmental applications.