Abstract This paper reported a successful preparation of CaCO3/anhydrite composites of anhydrite coated with nanosized CaCO3 by chemical precipitation route using the Ca(OH)2–H2O–CO2 reaction system. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and BET multiple-point nitrogen adsorption method. The results demonstrated that nanosized CaCO3 of 70 nm in average size was coated on the surface of anhydrite. The whiteness of the CaCO3/anhydrite composites can reach 85.8%, higher than that of the original anhydrite (63.1%). The surface of the CaCO3/anhydrite composites became rough without sharp edges, and its specific surface area was four times of that of the original anhydrite. This approach of surface nanocrystallization modification could ensure anhydrite an efficient application in the paper, rubber and plastic industries. A possible mechanism for coating of CaCO3 nanoparticles on the surface of anhydrite was also suggested.