N-isopropylacrylamide modified PEI (PEN) was synthesized via Michael addition and was developed as an efficient siRNA delivery system both in vitro and in vivo. PEN showed significant enhanced cytocompatibility compared with commercial PEI-25k. The complexation of PEN with siRNA was studied by gel retardation, particle size and zeta potential measurement. The in vitro transfection ability of PEN was measured by qRT-PCR assay, and achieved obviously enhanced gene silencing efficiency compared with PEI-25k. The confocal imaging and flow cytometric analysis further validated its excellent intracellular trafficking ability. For antitumor treatment experiment, PEN mediated siVEGF showed obviously therapeutic effects for the treatment of CT26 tumor. Therefore, the present study demonstrated a useful strategy for constructing efficient siRNA delivery vehicles for antitumor therapy.