Ob (obese) gene is supposed to regulate adipose tissue mass. However, it is still not completely clear how ob gene expression is regulated.Recently, it has been reported various stimuli which induce lipolysis, such as β-agonist and db cAMP, suppress ob gene expression. However, it is possible that these stimuli also activate cAMP response element binding protein (CREB) via A-kinase. Whether decrease of ob gene expression is induced by fatty acids accumulation by lipolysis or other, such as activation of CREB, we examined change in ob gene expression by induction of exogenous fatty acids accumulation which mimic accumulation of fatty acids by lipolysis.Loading of Triacsin C, an acyl CoA synthetase inhibitor, to the medium decreased the amount of ob mRNA (77% of control). Simultaneous addition of Triacsin C and chylomicron decreased the amount of ob mRNA further (53% of control). Loading of 2-bromopalmitate, a poorly metabolizable fatty acid derivative, also decreased the amount of ob mRNA (61% of control).From these results, it was suggested that intracellular fatty acids accumulation suppress ob gene expression in 3T3-L1 adipocytes.