A new method to modulate RAFT dispersion polymerization by introducing solvophilic homopolymers into the polymerization medium is proposed. It is discovered that in RAFT dispersion polymerization employing poly(4-vinylpyridine) trithiocarbonate macro-RAFT agent, the introduced solvophilic homopolymers of poly(N,N-dimethylacrylamide) (PDMA), poly(ethylene glycol), and poly(4-vinylpyridine) can greatly change both the size/morphology of poly(4-vinylpyridine)-block-polystyrene nanoassemblies and polymerization kinetics. RAFT dispersion polymerization decelerates with the increasing amount of introduced PDMA, and it favors formation of complex block copolymer nanoassemblies in the presence of PDMA. The possible reason for introduced solvophilic homopolymers affecting polymerization kinetics and the block copolymer nanoassemblies is discussed. Adding solvophilic homopolymers into the polymerization medium is believed to be a promising alternative to modulate RAFT dispersion polymerization.