In this paper, the groundwater sediment/titanium dioxide (Gs/TiO2) were prepared via a conventional calcination process using groundwater sediment from natural resource at Pasao, Uttaradit province, Thailand and commercial TiO2 as starting materials. The as–prepared were characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The photocatalytic activity toward the decomposition of agricultural residues (diazinon) at 247 nm was demonstrated under visible light irradiation for 120 min. The maximum experimental decomposition efficiency was 73.6% with the rate constant of 0.0102 min–1 for prepared Gs/TiO2 photocatalyst.