Grease composition and sealing device using same

A grease composition which is supplied between a plurality of lips provided in a sealing device that seals between a pair of members that rotate relative to each other, wherein

• the grease composition comprises a base oil (A), a thickening agent (B) and a rust preventive agent (C);
• the base oil (A) comprises more than 80% by mass and 95% by mass or less of the synthetic hydrocarbon oil and 5% by mass or more and less than 20% by mass of the synthetic ester oil based on the total base oil (A);
• and a kinematic viscosity of the base oil (A) at 40° C. is 30 to 80 mm2/s;
• the thickening agent (B) is a diurea compound represented by Formula (1);
• R1—NHCONH—R2—NHCONH—R3 (1)
• wherein R2 is a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms, R1 and R3 are a linear or branched alkyl group having 8 to 22 carbon atoms, and a content of groups other than a linear or branched alkyl group having 8 to 22 carbon atoms is 10 mol % or less based on the total mole number of R1 and R3, and
• the composition comprises 5 to 15% by mass of the thickening agent (B) and 0.1 to 2.0% by mass of the rust preventive agent (C) based on the total of the grease composition.