Textile dyeing wastewater becomes one of the root causes of environmental pollution. Titanium dioxide (TiO2) is one of the photocatalysts that shows prominent organic dye photodegradation ability. In this study, a porous tungsten oxide (WO3)/TiO2 composite was prepared through ultrasonic-assisted solvothermal technique with varying amounts of WO3 ranging from 0.25 to 5 weight % (wt.%). The prepared 0.50 wt.% WO3/TiO2 (0.50WTi) composite exhibited the highest photodegradation activity (4.39 × 10-2 min-1) and complete mineralization in chemical oxygen demand (COD) reading towards 30 mg.L-1 of Reactive Black 5 (RB5) dye under 60 min of light irradiation. Effects of large surface area, small crystallite size, high pore volume and size, and low electron-hole pair recombination rate attributed to the superiority of 0.50WTi. Besides, 0.50WTi could be reused, showing 86.50% of RB5 photodegradation at the fifth cycle. Scavenger study demonstrated that photogenerated hole (h+) was the main active species of 0.50WTi to initiate the RB5 photodegradation. Cytotoxicity assessment determined the readings of half-maximal inhibitory concentration (IC50) were 1 mg.mL-1 and 0.61 mg.mL-1 (24 and 72 h of incubations) for the 0.50WTi composite.