Co-electrospinning of polyacrylonitrile (PAN) and synthetic black iron oxide (Fe₃O₄), titanium oxide, cobalt oxide, and nickel nanoparticles was performed to prepare polymer composite nanofibers. The polymer composite nanofibers were heat treated at 250°C in the air to oxidize the PAN first. The fibers were then further heat treated at 500°C in argon gas to cause the PAN to be partially converted into carbon. The heat treated fibers contain carbon as the matrix and iron oxide (Fe₃O₄) titanium oxide, cobalt oxide, and nickel nanoparticles as the fillers. Photosensitive tests showed that the composite nanofibers possess the photovoltaic property in visible light. In ultra violet (UV) light, the composite fibers are not photosensitive. To coat the composite fibers with active carbon, some of the nanofiber samples were placed in a 10% dilution of sugar water in a non-stirred high pressure reactor to allow for hydrothermal carbonization. Several tests were applied to these coated samples. A light emission test was applied by using an electrochemical analyzer and a color-ink absorption test was applied by using a spectrometer. In addition to the photovoltaic test, a heat gun was used to test the thermoelectric property of the nanofibers. It has been found that all the active carbon coated nanofibers are sensitive to visible light, but not sensitive to UV light. The cobalt oxide particle filled nanonfiber shows strong thermoelectric property.