Biodegradable four-arm star-shaped poly(ethylene glycol)-block-poly(L-lactic acid) copolymer (sPEG-b-PLLA), four-arm star-shaped poly(L-lactic acid) (sPLLA), linearly poly(ethylene glycol)-block-poly(L- lactic acid) copolymer (PEG-b-PLLA) and linearly poly(L-lactic acid) (PLLA) were synthesized from L-lactice acid, pentaerythritol, poly(ethylene glycol) and star-shaped poly(ethylene glycol), using the method of melt polycondensation, and the products were characterized and confirmed by ¹H NMR spectroscopy, FT-IR and GPC.  Four types of ibuprofen loaded microspheres based on the above four types of polymers, i.e., IBU/PLLA, IBU/sPLLA, IBU/PEG-b-PLLA, and IBU/sPEG-b-PLLA microspheres were prepared using the method of solvent evaporation, and the optimized preparation technology was obtained via orthogonal experiments, and the drug-encapsulating properties and in vitro drug-releasing properties were studied.  The results showed that compared with IBU/PLLA and IBU/PEG-b-PLLA microspheres, the drug encapsulate efficiency of IBU/sPLLA and IBU/sPEG-b-PLLA microspheres were higher and the in vitro drug releasing rate slowed down, which mainly due to the faster degradation of sPLLA and sPEG-b-PLLA for the star-shaped structure and the block copolymerization of sPEG.  The drug releasing curves of these three types of microspheres could be fit by first-order equation, and the releasing mechanism was non-Fickian diffusing, i.e., the synergetic effect of polymer degradation and drug diffusion.