A modified double emulsion technique was adopted to prepare bovine serum albumin (BSA) loaded poly (D,L-lactic-co-glycolic acid) (PLGA) microspheres. In the formulations, polysorbates (Tween) such as Tween20(R), Tween40(R) or Tween80(R), instead of frequently used poly (vinyl alcohol) (PVA), was used as the emulsifier. Microspheres with porous surface, large particle size, low microsphere yield (similar to65.4%) and BSA entrapment efficiency (similar to25.2%) were obtained when Tween80(R) aqueous solution alone was used as the outer aqueous phase. However, microspheres with smooth surface, high yield and BSA entrapment efficiency could be produced successfully by introducing sodium chloride or glucose into the outer aqueous phase. Adding 5.0%(w/v) sodium chloride into the continuous phase led to increase in microsphere yield and BSA entrapment efficiency from 65.4% and 25.2% to similar to100% and 76.6%, respectively. Microsphere yield and BSA entrapment efficiency increased from 64.5% and 25.2%, to 97.2% and 89.3%, respectively, when 15.0%(w/v) glucose was added into the continuous phase. In constrast to the microspheres prepared in the presence of additive, a more marked burst release was observed for microspheres prepared without additive in the continuous phase, which may be attributed to the porous morphology of the latter.