Cobalt aluminate/carbon composite nanoparticles have been synthesised by utilising an auto-combustion method using glycine as an inexpensive fuel. The products were analysed by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), thermal analysis (TG), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectrum (DRS), energy-dispersive X-ray spectroscopy (EDS). The results exhibited that the average crystallite size of the as-prepared CoAl2O4/C nanocomposite was ca. 26 nm. The photocatalytic activity of the as-prepared catalyst was evaluated through the degradation of methylene blue (MB) dye under different conditions, and the photocatalytic degradation mechanism was proposed. The results indicated that CoAl2O4/C nanocomposite has a high catalytic performance for the photocatalytic degradation of MB dye under UV illumination in the presence of H2O2. The degradation efficiency reached 98.5% in 90 min with a degradation rate constant of 0.046 min−1.