Abstract: The compatibilities of molybdenum dialkyldithiocarbamate(MoDTC)and Cacompounds in greases were studied. The physical and chemical properties of Li-or Cabase grease are slightly affected by adding MoDTC and Ca-compounds. Tests in Four Ball and Amsler type testers show that MoDTC and calcium petroleum sulfonate or calcium carbonate are synergic on wear-reducing or load-carrying capacity respectively.Low friction coefficient, wear-mitigating and EP properties are attributed to the surface film that consists of MoS_2, MoO_3, FeS_2, CaCO_3 and CaSO_4 found by AES and XPS. The microhardness of worn surface varies with the kind of Ca-compounds.