© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The degradation and mineralization of azo dye acid red 14 by Titanium dioxide (TiO2) photocatalysis under simulated solar light was studied at lab scale. The characteristics (such as phase features, specific surface area, bandgap energy, etc.) of nanosized TiO2 were investigated in detail. The color removal rate, decrease rate of total organic carbon, and production rate of sulfate ions in aqueous solution were determined. Acid red 14 could be decolorized and mineralized efficiently with nanosized TiO2 under simulated solar light. Acidic or neutral conditions were beneficial to the decolorization of acid red 14 aqueous solutions. Acid red 14 was nearly 100% mineralized after 60min irradiation by simulated solar light under certain experimental conditions. The photocatalytic degradation efficiency increased with increasing the irradiation intensity of solar simulated light. TiO2 dosage, pH value of aqueous solution, and initial concentration of acid red 14, had significant influences on the decolorization efficiency. It is feasible to use photocatalysis with nanosized TiO2 under simulated solar light to efficiently degrade and mineralize acid red 14. The high photocatalytic efficiency of TiO2 under simulated solar light might be related to its lower bandgap energy and the relatively higher fraction of anatase phase. Acid red 14 could be mineralized by nanosized TiO2 suspension under simulated solar light by nearly 100% after 60min irradiation under certain experimental conditions. While TiO2 dosage, pH, and initial acid red 14 concentrationhad significant effects on the decolorization efficiency, the photocatalytic degradation efficiency increased with the enhancement in irradiation intensity. The high photocatalytic efficiency of this nanosized TiO2 under simulated solar light might be related to its lower bandgap energy and the relatively higher content of anatase phase.