Spherical unimolecular amphiphilic branched A-B block copolymer nanoparticles in methanol are fabricated via thermal annealing using the methanolic upper critical solution temperature (UCST) of the hydrophobic block segment. These polymer nanoparticles are then used to produce an aqueous poorly water-soluble drug nanoparticle suspension with a mass : drug ratio of 1 : 1 and 100% nanoparticle yield. The drug nanoparticles in the suspension are stabilized by multiple polymer nanoparticles.