PURPOSE: To obtain a lubricant additive composition capable of establishing and maintaining a substantially constant static breakaway coefficient of friction between a pair of friction surfaces that are periodically frictionally engaged with each other by combining two specific additive components.

CONSTITUTION: The lubricating additive composition is prepared by blending at least (A) a hydroxyalkyl aliphatic imidazoline in which the hydroxyalkyl group contains 2-4 carbon atoms, and in which the aliphatic group is an acyclic hydrocarbyl group containing 10-25 carbon atoms and (B) a di(hydroxyalkyl) aliphatic tertiary amine in which the hydroxylakyl groups, being the same or different, contain each 2-4 carbon atoms, and in which the aliphatic group is an acyclic hydrocarbyl group containing 10-25 carbon atoms, in a molar ratio of 0.005-0.50 mole of component A per mole of component B. The lubricant additive composition in an amount necessary for friction modification is added to an oil having lubricating viscosity to obtain a lubricant composition.