In this work, beta-Bi2O3 was synthesized by Pechini method and its photocatalytic performance was compared with a commercial oxide. Catalysts were characterized by ultraviolet diffuse reflectance spectroscopy (DRS-UV), X-ray diffraction (XRD), scanning electron microscopy (SEM) and textural analysis by N-2 physisorption. Photocatalytic activity was tested under UV-vis light on the degradation of isoniazid, an antibiotic used in tuberculosis disease. Effects of pH and catalyst loading were evaluated and better results were achieved at pH 7 using 1.0 g L-1 of catalyst. beta-Bi2O3 synthesized (S-Bi2O3) presented a higher mineralization percentage and stability during photocatalytic treatment than the commercial oxide (C-Bi2O3). Photo-holes were identified as the main reactive species responsible for the isoniazid oxidation. By-products were identified by electrospray ionization mass spectrometry (ESI-MS) and the incomplete mineralization (24% mineralization in 2 h) was explained by the presence of those compounds. Toxicity of isoniazid was assessed against Vibrio fischeri and it was reduced after photocatalytic oxidation in both, deionized water and real wastewater as matrix. Antimycobacterial activity against Mycobacterium tuberculosis was inhibited after 150 min when complete isoniazid degradation was achieved. Results indicated that photocatalytic treatment with Bi2O3 is a suitable method to eliminate contaminants such as isoniazid and reduce environmental risk to aquatic life.