In this study,poly(lactide-co-glycolide) (PLGA) porous microspheres were fabricated by double emulsion method using ammonium bicarbonate as gas-foaming agent.Bovine serum albumin (BSA) was encapsulated into porous PLGA microspheres as modeling protein.Single factor experiment was performed to study the effects of different factors on the morphology and the water uptake ratio of porous microspheres.The investigated variations included the type of emulsifying agent and organic solvents,concentration of PLGA,PVA and gas foaming agent,volume ratio of W1/O,osmotic pressure of W l phase,stirring rate and rate of homogenizing.These porous microspheres were characterized for particle size,average pore size,morphology and water uptake ratio Orthogonal experiment was performed to study the influence of different factors.The optimized porous PLGA microspheres were 451μm in size of microspheres,19.30μm in size of surface pores,58.53% in encapsulation of BSA and 700% in water uptake ratio.The sustained release of BSA lasted for 30d with a burst release of 34% at the first day.