Biodegradable poly(propylene carbonate) (PPC) matrix composite with a significant improvement in yield strength was successfully prepared by incorporating a low content of poly(methyl methacrylate) (PMMA) via a supercritical carbon dioxide route. Atomic force microscopy measurement shows that the size of the dispersed PMMA phase in the PPC substrate is in the range from 50 nm to 200nm, which is much smaller than the smallest ones that can be obtained by conventional melt blending method. Tensile tests demonstrate the excellent mechanical properties of the composites prepared in this study. By incorporating only 5 wt% PMMA, the obtained composites show approximately 4 times higher yield strength than pure PPC and the elongation at break of the composites is well remained. By comparing with the reported works, this method shows the highest enhancement efficiency of PPC. The significant reinforcement of PPC is ascribed to the nano size phase-separated domains of rigid PMMA. These findings show an effective modification method of PPC for the potential alternative to the non-biodegradable polymers. (C) 2013 Elsevier B.V. All rights reserved.