This invention relates to substance FKI-3864 represented by the following formula [I] having an inhibitory activity on the synthesis of triacylglycerols and a method for preparing the same. The substance FKI-3864 can be prepared by a method comprising culturing a microorganism which belongs to the genus Penicillium and is capable of producing the substance FKI-3864, and particularly Penicillium pinophilum FKI-3864 (FERM BP-11093) so as to accumulate the substance FKI-3864 in the culture and collecting the substance FKI-3864 from the culture. The substance has an inhibitory activity on the synthesis of intracellular triacylglycerols and is useful for prevention or treatment of obesity.