Water-soluble polysaccharides (WSPSs) have been isolated from the fruit and leaves ofAronia melanocarpa Elliot (black chokeberry) plants treated with chlorocholine chloride in various concentrations. It has been established that they are composed of galacturonic acid and the neutral monosaccharides galactose, glucose, arabinose, xylose, and rhamnose. In addition, another two unidentified spots of monosaccharides or their derivatives were found in the polysaccharides of the fruit, and one in those of the leaves. The ratios of the neutral monosaccharides in the WSPSs have been determined. Accumulation of the polysaccharides under the influence of various concentrations of chlorocholine chloride has been studied. It has been established that the retardant used (chlorocholine chloride) increases the accumulation of polysaccharides in the fruit by a factor of 1.5–2, but no appreciable accumulation of them was observed in the leaves.