Regarding the photocatalytic ability of titanium dioxide (TiO2) nanoparticles, poly(methyl methacrylate) (PMMA)/TiO2 nanofiber mat was studied and the photocatalytic activity of the composite system was determined from degradation of a model dye, methylene blue. For this purpose, TiO2 nanoparticles in crystal phase was synthesized and immobilized in PMMA nanofiber mat using via electrospinning process. FTIR and UV-VIS spectroscopy, SEM and water contact angle measurements were utilized to characterize PMMA/TiO2 nanofiber mat and to compare the composite nanofiber mat with that of pure PMMA nanofiber mat. The immobilization of TiO2 nanoparticles in PMMA nanofiber mat yielded thicker nanofibers with less beaded fiber structures. In addition, the introduction of TiO2 nanoparticles enhanced the photocatalytic decomposition of methylene blue in the ambient air under ultraviolet light irradiation.