The photocatalytic degradation of textile wastewater containing Reactive Black 5 (RB5) azo dye was investigated by using immobilized TiO₂ nanofiber-nanoparticle composite catalyst on glass plates. The process was studied by monitoring the change in RB5 concentration, depletion in total organic carbon (TOC) and by determining the intermediate products using UV-visible spectrophotometry and gas chromatography-mass spectrometry (GC-MS) techniques. After immobilization, the composite shows higher photocatalytic activity for degradation of RB5 than that of nanoparticle thin-film layer under UV irradia-ion. Complete decolorization was achieved in 120 min, corresponding to organic degradation with a reduction in TOC after 300 min of UV irradiation by 91%. The photocatalytic degradation mechanism of RB5 was proposed based on the identified compounds by GC-MS technique, showing the destruction of the azo dye structure, which became smaller molecular mass compounds. The degradation slightly decreased after multiple reuse of composite catalyst during photocatalytic treatment. The recovery of its photocatalytic performance was obtained through reannealing.