TiO₂-embedded carbon nanofibers were prepared by electrospinning method. Polyacrylonitrile (PAN) solution containing TiO₂ was electrospunned (TiO₂/PAN) and subsequently calcined under N₂ atmosphere, which resulted in the carbonization of PAN polymer (TiO₂/CNF). And then carbonized composite fibers further oxidized by thermal treatment under oxidative condition (Oxi.-TiO₂/CNF). Gaseous CH₃CHO was efficiently degraded and CO₂ was simultaneously produced on Oxi.-TiO₂/CNF compoistes under UV illumination. Although UV-illuminated TiO₂/PAN composites could also oxidize gaseous CH₃CHO, they slowly degraded themselves. On the other hand, TiO₂/CNF had no effect on the photocatalytic oxidation of CH₃CHO, which was due to the reduction and phase transformation of TiO₂ during carbonization. XPS results show that TiO₂ was partly reduced by carbonization and then oxidized by post-oxidation process. There was no anatase phase of TiO₂ in TiO₂/CNF composites whereas anatase phase of TiO₂ was obviously observed in Oxi.-TiO₂/CNF composites. Moreover, BET surface area was hightly enhanced by post-oxidation process, which was responsible for the adsorption of gaseous CH₃CHO on Oxi.-TiO₂/CNF. Therefore, post-oxidation process affects not only oxidation but also surface modification of carbon nanofibers.