PURPOSE: To obtain a succinimide dispersant passing an ASTM sequence VE engine test, not deteriorating a fluoroelastomer part and added to lubricant by reacting a specific acylating agent with polyamine over two stages.

CONSTITUTION: This succinimide dispersant is prepared by a method wherein at least one kind of polyamine is a succinic acid acylating agent substd. by at least one kind of an acyclic hydrocarbyl group and at least 70 in the number of carbon atoms of its substituent on an average (i) and the obtained product is reacted with aliphatic adjacent dicarboxylic acid acylating agent having 4-6 carbon atoms (excepting carbon atoms of esterified alcohol in the case of ester) in its molcule (ii). At this time, the acylating agent is used in an amt. of 1.05-2.85 times mol of polyamine in the process (i) and the acylating agent is used so as to become 3.05 times mol of polyamine in total in the process (ii).