Pure and aluminium-doped tin oxide (SnO2) nanoparticles have been successfully synthesized by a sol-gel method. The paper mainly reports an investigation on the effect of a non-ferromagnetic dopant (aluminium) on the magnetic properties of SnO2 nanoparticles. The structural and optical properties were also examined. The as-prepared nanoparticles were characterized using X-ray diffraction (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), UV-vis spectroscopy and magnetic characterization using a vibrating sample magnetometer (VSM). XRD data revealed the SnO2 phase formation for all the samples, indicating that the growth technique was efficient in diluting aluminium ions in the SnO2 lattice. All the samples exhibited peculiar room-temperature ferromagnetic behaviour. The origin of ferromagnetism in the samples lays around the Al–SnO2 interfaces and vacancy defects. © 2017, Springer Science+Business Media New York.