Abstract: The invention provides a magneto-rheological grease composition which contains (a) a base oil including at least 30% by mass of an ether type synthetic oil; (b) an aliphatic diurea thickener; and (c) magnetic particles in an amount of 45 to 95% by mass based on the total mass of the composition. The magneto-rheological grease composition can show superior thermal stability, dispersion stability and magneto-rheological properties.

Abstract: The invention provides a grease composition for constant velocity joint containing the components (a) to (g) below and a constant velocity joint containing said composition. (a) a diurea thickening agent having the following formula (1): R1NH—CO—NH—C6H4-p-CH2—C6H4-p-NH—CO—NHR2 ??(1) wherein R1 and R2 may be the same or different and represent C8-C20 alkyl groups, (b) an ester synthetic oil, (c) a mineral oil and/or a synthetic hydrocarbon oil, (d) a molybdenum dialkyldithiocarbamate, (e) molybdenum disulfide, (f) a polytetrafluoroethylene, and (g) a zinc dithiophosphate compound. The grease composition of the invention reduces variations in rotational resistance of the constant velocity joint at a low temperature.