Three UV-sensitive, hyperbranched-poly(siloxysilane)-based polymeric photoinitiators, bearing an alkyl phenone moiety linked to the surface of the hyperbranched polymer, were synthesized via the hydrosilylation of hyperbranched poly(siloxysilane) and modified UV-sensitive compounds. Hyperbranched poly(siloxysilane) was prepared via the polyhydrosilylation of the AB(2)-type monomer methyl vinyl dichlorosilane. The chemical structures of the polymeric photoinitiators were characterized with H-1, C-13, and Si-29 NMR, elemental analysis, Fourier transform infrared, differential scanning calorimetry, UV spectrophotometry, and thermogravimetric analysis. The UV-curing behaviors of the blends of the hyperbranched polymeric photoinitiators with UV-curable epoxy acrylate (EA) resin were determined by Fourier transform infrared, and the results showed that the initiation efficiency of the polymeric photoinitiators was excellent and that the thermostability of the EA/polymeric photoinitiator curing systems was higher than that of the EA/pbotoinitiators.