Platinum microcoils coated with immobilized recombinant human vascular endothelial growth factor (rhVEGF) were prepared and the effectiveness for the embolization of aneurysms was investigated using a rat model. Platinum coils were prepared by successive deposition of cationic polyethyleneimine and anionic heparin, and VEGF was immobilized through affinity interaction with heparin. Unmodified, heparin-coated, or rhVEGF-immobilized platinum coil segments were inserted into the ligated external carotid arteries at the bifurcation of the common carotid artery (CCA) of adult female rats. The bifurcation segments of the CCA were harvested 2 weeks after the coil placement. rhVEGF-immobilized coils showed significantly greater endothelial formation at the aneurysm orifice and cell infiltration in the aneurysm body compared with the unmodified and heparin-coated coils. The percentage of sac occlusion was significantly greater in the rhVEGF-immobilized group (77.53 +/- 27.58%) than in the heparin-coated group (44.81 +/- 38.30%) and unmodified group (34.99 +/- 28.15%). Scanning electron microscopy showed a tendency for more fibrotic and cellular collections on the coil surface and more tissue mass filling in the coil lumen in the rhVEGF-immobilized group. Platinum microcoils coated with immobilized rhVEGF may be effective for the obliteration of aneurysms.