Applicability of methyl propionate to microencapsulation was evaluated with regard to volatility, capability of forming emulsions, and their quality. An emulsion-based technique was then developed to encapsulate progesterone into poly-D,L-lactide-co-glycolide microspheres. Their characteristics were compared with those prepared using ethyl acetate. Our results demonstrated that methyl propionate had greater evaporative tendency and less water miscibility than ethyl acetate did. The former allowed us to prepare good microspheres. Their average volume mean diameter was 68.3 +/- 1.7 mu m with a span index of 0.91 +/- 0.13. Progesterone did not undergo polymorphic transition during microencapsulation, and its encapsulation efficiency ranged from 41.80 +/- 1.83 to 85.64 +/- 1.95%. Residual methyl propionate in various microspheres was found to be 0.97 +/- 0.03 to 1.54 +/- 0.07%. Such microsphere characteristics were quite similar to those prepared by the ethyl acetate-based microencapsulation process. Overall, our findings reflect that methyl propionate has a potential to become an invaluable solvent for microencapsulation.