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Hydroxyl-functionalized three-arm poly(_-caprolactone)s (PGCL-OHs) were synthesized by the ring-opening polymerization of _-caprolactone in the presence of glycerol (as the core) and stannous octoate. The effect of the feed ratio of _-caprolactone to glycerol on the ring-opening polymerization was studied. These three-arm PGCL-OHs were then converted into double-bond-functionalized three-arm poly(caprolactone)s (PGCL-Mas) by the reaction of PGCL-OH with maleic anhydride in the melt at 130 °C. The quantitative conversion of hydroxyl functionality was achieved at a low molecular weight. The resulting PGCL-OH and PGCL-Ma were characterized with gel permeation chromatography, Fourier transforminfrared, 1H NMR, 13C NMR, and differential scanning calorimetry.