PURPOSE: To obtain a lubricant compn. providing lower amount of sulfate ash while satisfying a standard of high performance by composing a lubricating viscosity oil, a carboxylic acid dispersant component, a nonionic surfactant, etc., and a specific hydrocarbyl substd. phenol.

CONSTITUTION: A low ash lubricant oil contains (A) major amount of a lubricating viscosity oil, (B) 0.5-5 wt.% (pref. 1-4 wt.%) a carboxylic acid dispersant component (a reaction product of a hydrocarbyl acid substd. succinic acid product and a polyamine), (C) (1) a nonionic surfactant, (2) pref. 0.04-2% a mixture of a hydrocarbyl substd. carboxylic acid, and its derivatives in the ratio 90:10-10:90 and (D) 0.1-10% (pref. 1-4%) of a hydrocarbyl substd. phenol prepared without using a reaction product contg. active sulfur or chlorine, and furthermore contains an acid functional or a phenol functional material (reacted with a basic metals so that the whole sulfate ash content of the composition is adjusted to 0.25-1%).