An abundant class of synthetically colored organic compounds is azo dye, which is characterized by the presence of one or more azo groups (-N=N-) linked between aromatic rings. The release of this coloring agent to the environment causes a severe wastewater problem. Photocatalysis is an efficient technique for removing these dye pollutants because of its several advantages. The most widely used semiconductor photocatalyst is titanium dioxide (TiO₂) due to its comparatively high photocatalytic efficiency. In this work, several operational parameters affecting the photocatalytic degradation of mixtures of two azo dyes—Acid Yellow 23 (AY) with 1 azo group and Acid Black 1 (AB) with 2 azo groups—including types of dye, initial dye concentration, photocatalyst dosage, dissolved oxygen level, initial solution pH, and water hardness concentration, were investigated by using a mesoporous-assembled TiO₂ nanocrystal photocatalyst. The experimental results showed that for the mixture of AY and AB, the λ_max values of both dyes from UV-visible spectroscopy do not change upon their mixing at different irradiation times during the course of photocatalytic degradation. At AY and AB concentrations of 5 and 2.5 mg/l, the optimum conditions were a photocatalyst dosage of 10 g/l, a dissolved oxygen level of 37.7 mg/l, and an initial solution pH of 4.5, providing the highest degradation rate of azo dyes. Moreover, water hardness negatively affected the degradation performance.