Multicompartment nanoparticles (MCBNs) constructed with the brush block terpolymer of [poly(p-chloromethylstyrene)-graft-poly(4-vinylpyridine)]-block-polystyrene (PCMS-g-P4VP)-b-PS are prepared through dispersion polymerization of styrene in the methanol/water mixture mediated by the brush macro-RAFT agent of poly(p-chloromethylstyrene)-graft-poly(4-vinylpyridine) trithiocarbonate. During the dispersion RAFT polymerization, the molecular weight of the brush (PCMS-g-P4VP)-b-PS block terpolymer linearly increases with the monomer conversion. Ascribed to the brush (PCMS-g-P4VP) block, MCBNs including a PS core and discrete subdomains of (PCMS-g-P4VP) on the PS core dispersed in water are formed. The reasons leading to formation of MCBNs are discussed, and the immiscibility of the brush (PCMS-g-P4VP) block with the PS core, the low number density of the brush (PCMS-g-P4VP(25))(21) chains tethered on per surface area of the PS core, and the high molecular weight but the low polymerization degree of the brush (PCMS-g-P4VP) block are ascribed. Au nanoparticles are immobilized on the bulgy PCMS-g-P4VP subdomains on MCBNs and show high catalytic efficiency in the aerobic alcohol oxidation.