Interpenetrating polymer networks (IPNs) Poly(styrene-butadiene-styrene)/Poly(n-butyl methacrylate-b-methyl acrylate) (SBS/PBMA-b-PMA) was prepared by atom transfer radical polymerization (ATRP) and characterized by FT-IR, 1H NMR and TEM. The TEM photos illustrated that SBS/PBMA-b-PMA formed an obvious core-shell structure, with cross-linked SBS/PBMA core and linear PMA shell. The compatibility of IPNs with PVC was studied using SEM and DSC instruments. The mixed polymers displayed one Tg (Tg=79.4°C, ΔTg=32.5°C) and showed good compatibility. The SEM fracture surface morphologies displayed partial feature of ductile fracture different form neat PVC.