In this paper, highly electrically conductive polymeric composites were obtained by low-temperature expandable graphite (LTEG) filling poly(L-lactic acid) in the presence of ascorbic acid via an in situ exfoliation and subsequent reduction process during the melt blending. The electrical conductivity of the poly(L-lactic acid)/reduced and expanded graphite (PLLA/R-EG) composites was determined by a two-point probe resistivity determiner and compared with that of the poly(L-lactic acid)/expanded graphite (PLLA/EG) composites. The percolation threshold of PLLA/R-EG blends decreased from 11.2 wt% to 7.1 wt%, which illustrated the superiority of R-EG to the electrically conducting ability of PLLA composites. At the graphite concentration near the percolation threshold, the electrical conductivity of PLLA/R-EG composites was much higher than that of PLLA/EG composites. The effective in situ expansion and reduction of LTEG was crucial to the overall electrical conductivity of the blends, which was confirmed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. Dynamic rheology analysis confirmed that the connected networks that were the major cause of the rapid increase in electrical conductivity were much more easily formed for PLLA/R-EG blends than those of PLLA/EG blends. Thermogravimetric analysis (TGA) was applied to determine the decomposition and thermal stability of the PLLA/R-EG composites.