The purpose of this research was to improve the photocatalytic breakdown of methylene blue (MB), which is driven by visible light by synthesizing and characterizing NiO/CuBi2O4 nanocomposites. The nanocomposites were synthesized via a grinding-annealing method, and their structural, optical, and photocatalytic properties were thoroughly investigated. The key method involved evaluating the breakdown of MB when it is exposed to visible light in order to determine the photocatalytic activity, optimizing the NiO/CuBi2O4 mass ratio and catalyst mass. Important findings revealed that the NiO/CuBi2O4 nanocomposite, particularly at a 2:1 mass ratio and 10 mg catalyst loading, exhibited significantly higher photocatalytic activity (74.12 % degradation) compared to pure NiO (34.16 %) and CuBi2O4 (64.35 %). The improvement in performance was linked to the nanocomposite's ability to lower the NiO bandgap. Kinetic analyses validated that the photodegradation process adhered to a pseudo-first-order model, with the nanocomposite exhibiting the fastest reaction rate (6.07 × 10⁻³ min⁻¹). Ultimately, the NiO/CuBi2O4 nanocomposite proves to be a highly promising, sustainable catalyst for dye breakdown under visible light, presenting a viable strategy for cleaning up contaminated environments. © 2025 Elsevier B.V.