PURPOSE: To provide an improving agent for an oily composition which consists of a specified oil-soluble ethylene copolymer, organic polyamine, etc., and the reaction product of poly-n-butene substituted dicarboxylic acid substance and exhibits improved low temperature viscometric properties.

CONSTITUTION: This improving agent comprises (A) an oil-soluble ethylene copolymer which consists of (i) approximately 15-90 wt.% ethylene and (ii) approximately 10-85 wt.% 3-28C α-olefin, has number average molecular weight of approximately 5,000-500,000, and is grafted with an etylenically unsaturated carboxylic acid substance having 1-2 carboxylic (anhydride) groups, (B) an organic polyamine having reactive amine groups consisting of primary or secondary amine groups or a polyol, and (C) the reaction product of poly-n-butene substituted dicarboxylic acid of approximately 300-3,000 number average molecular weight.