The aim of this study was to fabricate deformable chitosan (CS) microspheres for arterial embolization. CS microspheres containing poly(ethylene glycol) (PEG) were prepared by ionotropic gelation; PEG was then removed from the CS microspheres to produce the highly porous structure to allow deformability. The porosity was controlled by blending ratios of CS/PEG polymers (CS/PEG=from 100/0 to 15/85) and the effect of porosity on microcatheter delivery was examined. The size range of porous microspheres was 500—600 μm with sphericity between 1.012—1.041. Scanning electron microscope observation confirmed that microporous networks were effectively obtained by PEG extraction proportional to the initial amount of PEG. Water retention capacities, indicative of internal porosities of microspheres, increased with increasing initial amounts of blended PEG. CS microspheres with water retention values of greater than 28% exhibited noticeable deformation and smooth passage through the microcatheter tip. Novel deformable microspheres are, therefore, expected to be clinically applicable for arterial embolization.