A novel approach of in situ polymerization and in situ compatibilization was adopted to prepare the nano-blend of poly (2,6-dimethyl-1,4-phenylene oxide) (PPO), polystyrene (PS) and polyamide 6 (PA6). Anionic ring-opening polymerization of epsilon-caprolactam was carried out in the presence of PPO and PS. And PS, the chain of which bore methylmethacrylate (MMA) groups, acted as macroactivator to initiate PA6 chain growth from the PS chain and formed a graft copolymer of PS and PA6 and pure PA6 simultaneously. Thus the nano-structured PA6 dispersed phase in the PPO matrix could be achieved.