<p>Nano-sized calcium carbonate and micro-sized graphite are commonly used additives in calcium sulfonate grease. It is worth studying how the two additives together affect the tribological properties in the complex oil-soap structure of calcium sulfonate grease. Regarding this issue, nano-sized CaCO₃ and micro-sized graphite blends in different proportions were selected to investigate the lubrication performance. A combination of 1 wt% micro-sized graphite and 5 wt% nano-sized CaCO₃ contributed the excellence friction-reducing and anti-wear compared to the calcium sulfonate grease without additives or the calcium sulfonate grease with above additions alone. The additive blends could be synergistic to take part in chemical reactions on the Hertz contact area and form films to maintain a low friction state during whole friction process.</p>