||Poly(N-vinylamine)(PVAm) is an interesting polymer having a large amount of primary amine groups, but there has been only few reports regading the controlled radical polymerization. We synthesized poly(4-hydroxystyrene)–b-poly(N-vinylamine)(PHS-b-PVAm) by Reversible Addition Fragmentation Chain-Transfer(RAFT) polymerization. We use ‘switchable’ RAFT agent to polymerize precursor polymer; poly(4-acetoxystyrene)-b-poly(N-vinylformamide)(PAcOS-b-PNVF). The reactivity of C-S double bond on the switchable RAFT agent can be controlled by protonation/deprotonation of pyridinyl Z group which gives a proper control for the polymerization of both PAcOS and PNVF blocks. PHS-b-PVAm has an acidic phonolic group on the PHS block and a basic primary amine group on the PVAm block. The diblock polymer undergoes self-assembly in water, forming spherical nanoparticles. The self-assembled nanoparticle shows double pH-responsive character; the particle size changes in both acidic and basic condition.