The invention provides a grease composition used for lubricating a mechanical part having a steel portion to be lubricated which performs a rolling motion and a rolling and sliding motion, containing a base oil, a thickener and an additive, wherein the additive includes at least one compound selected from the group consisting of polyethylene wax, oxidized polyethylene wax, polypropylene wax, montan wax and amide wax.

Provided is a grease composition including a base oil (A) containing an alkyl naphthalene (A1) and an aliphatic diurea (B) represented by general formula (b1):
R.sup.1—NHCONH—R.sup.3—NHCONH—R.sup.2  (b1) (wherein, R.sup.1 and R.sup.2 each independently represent a monovalent aliphatic hydrocarbon group having 9 to 20 carbon atoms, and R.sup.3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms), wherein a content of the aliphatic diurea (B) is 20 to 30% by mass based on a total amount of the grease composition.

The invention provides a grease composition used for lubricating a mechanical part having a steel portion to be lubricated which performs a rolling motion and a rolling and sliding motion, containing a base oil, a thickener and an additive, wherein the additive includes at least one compound selected from the group consisting of polyethylene wax, oxidized polyethylene wax, polypropylene wax, montan wax and amide wax.

Provided is a grease composition including a base oil (A) containing an alkyl naphthalene (A1) and an aliphatic diurea (B) represented by general formula (b1):

R.sup.1NHCONHR.sup.3NHCONHR.sup.2(b1)

(wherein, R.sup.1 and R.sup.2 each independently represent a monovalent aliphatic hydrocarbon group having 9 to 20 carbon atoms, and R.sup.3 represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms),

wherein a content of the aliphatic diurea (B) is 20 to 30% by mass based on a total amount of the grease composition.