Dye-sensitized solar cells (DSSCs) have become an important solar energy conversion system. The development of DSSC structures that use lightweight and flexible plastic substrates is very important for their actual use as solar energy conversion devices in urban life. The greatest obstacle to the application of lightweight flexible substrates to DSSC is the preparation of mechanically robust TiO2-based nanoporous working electrode layers without a sintering process. This paper presents a novel nanofiber/nanoparticle composite structured TiO2 working electrode fabricated without a sintering process; instead, TiO2 paper, consisting of TiO2 nanofibers, is inserted into the TiO2 nanoparticle-based electrode. TiO2 nanofiber paper was prepared by direct electrospinning from TiO2 sol solution without polymer additives, followed by redispersion, filtering, and heat treatment to yield well-crystallized and mechanically flexible paper. Insertion of TiO2 nanofiber paper into the electrode prevented cracking of the TiO2 nanoparticle-based sinter-free electrode like composite materials toughened by fibers. At the same time, well-sintered TiO2 nanofibers improved energy conversion efficiency compared to conventional TiO2 nanoparticle sinter-free electrodes.