Biodegradable polymers have been widely used as scaffolding materials to regenerate new tissues. To mimic natural extracellular matrix architecture, a novel highly porous structure, which is a three-dimensional interconnected fibrous network with a fiber diameter ranging from 50 to 500 nm, has been created from biodegradable aliphatic polyesters in this work. A porosity as high as 98.5% has been achieved. These nano-fibrous matrices were prepared from the polymer solutions by a procedure involving thermally induced gelation, solvent exchange, and freeze-drying. The effects of polymer concentration, thermal annealing, solvent exchange, and freezing temperature before freeze-drying on the nano-scale structures were studied. In general, at a high gelation temperature, a platelet-like structure was formed. At a low gelation temperature, the nano-fibrous structure was formed. Under the conditions for nano-fibrous matrix formation, the average fiber diameter (160-170 nm) did not change statistically with polymer concentration or gelation temperature. The porosity decreased with polymer concentration. The mechanical properties (Young's modulus and tensile strength) increased with polymer concentration. A surface-to-volume ratio of the nano-fibrous matrices was two to three orders of magnitude higher than those of fibrous nonwoven fabrics fabricated with the textile technology or foams fabricated with a particulate-leaching technique. This synthetic analogue of natural extracellular matrix combined the advantages of synthetic biodegradable polymers and the nano-scale architecture of extracellular matrix, and may provide a better environment for cell attachment and function.