The morphologies and properties of poly(D,L-lactic acid)/carbon nanocapsule (CNCs) electrospun fiber mats were studied. To determine the effect of filler, a solution without sufficient entanglement density was used. The rheological results showed that the solution entanglement density was enhanced by the addition of filler, which led to the formation of network between the polymer chains and filler particles. The findings can be used for further exploration of electrospinning in semidilute solutions. The electrical conductivities of electrospun fiber mats and cast films were determined and fitted using the percolation theory. When the CNC content was above the critical percolation concentration, a master curve was obtained provided that the conductivity curves were normalized with the level of percolation network. The porosity effect was investigated. In addition, the microstructure of as-spun composite fiber was examined in detail. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128:958-969, 2013