To provide compositions for increasing the solubility and stability of solute compounds therein, and more particularly compositions including highly branched polysaccharides that may be used to improve solubility, stability, and/or bioavailability of solute compounds for the food, nutraceutical, personal care, skin care, cosmetics, pharmaceuticals, medical, paint and coating, and agricultural industries.SOLUTION : The present invention provides a composition having highly branched α-D-glucan or a modified form thereof, and a solute compound having improved water solubility compared to the case of the highly branched α-D-glucan being absent. The composition is used for improving the solubility of the solute compound.SELECTED DRAWING : None