In this study, Bi2O3-Co3O4 composite oxides were prepared and their catalytic efficiency to activate peroxymonosulfate (PMS) towards the degradation of Acid Orange 7 dye (AO7) was evaluated. The characterization of the synthesized catalysts was carried out by XRD, TEM, XPS, FT-IR, and ICP-OES analyses. The increased basicity of the Bi2O3-Co3O4 hybrids contributed to the much better catalytic activity in PMS activation resulting in a considerably higher rate of AO7 degradation compared to that obtained with bare Co3O4. The sample with 50 wt.% Bi2O3 showed the best performance under a broad pH range with very low Co leaching of 72 mg/L even under acidic conditions. Degradation of 50 mg/L AO7 reached almost 100% within a short duration of 12 min by using very low catalysts concentration of 0.1 g/L and [PMS]/[AO7] = 6. The influence of the Bi2O3 content, catalyst dosage, molar ratio of [PMS]/[AO7], initial pH, and temperature on AO7 degradation were studied. Surface-bound sulfate radicals generated in the Bi2O3-Co3O4/PMS oxidation system were proved as the predominant radical species through radical quenching experiments.