To obtain an ACAT inbibitor having acylcoenzyme A cholesterol acyltransferase(ACAT) inhibitory activity and suitable in e.g. preventing/treating arteriosclerosis by including a specific saponin.

This ACAT inhibitor is obtained by including a saponin shown by the formula (R1 is a saccharide residue; R2 to R5 are each H, OH or a 1-4C alkyl; R6 is H or a saccharide residue; dotted line means a bond which may be present or absent) which is afforded by the following procedure: water is added to leaves of Ilex kudincha followed by reflux under heating for 2 h and then cooling, the resulting system is subjected to filtration to remove insolubles, the resulting filtrate is lyophilized and then charged into an adsorptive resin column followed by eluting the adsorbed matter with methanol, the resulting eluate is concentrated and then purified through e.g. reversed-phase high-performance liquid chromatography.