Ghrelin is an appetite-stimulating peptide hormone with an octanoyl modification at serine 3 that is essential for its orexigenic effect. Ghrelin O-acyltransferase (GOAT) is the enzyme that catalyzes ghrelin acylation using fatty acyl-coenzyme A as a substrate. We previously developed an assay system based on the AGS-GHRL8 cell line that produces octanoylated ghrelin in the presence of octanoic acid, and demonstrated that some fatty acids suppressed octanoylated ghrelin production. Recent studies have reported that triterpenes have anti-obesity effect. Since such triterpenes, like fatty acids, have a carboxyl group, we speculated that they can suppress octanoylated ghrelin production. To test this hypothesis, we investigated the effect of triterpenes on octanoylated ghrelin production. Asiatic acid, corosolic acid, glycyrrhetinic acid, oleanolic acid and ursolic acid suppressed octanoylated ghrelin levels in AGS-GHRL8 cells without decreasing transcript expression of GOAT or furin, a protease required for ghrelin maturation. β-amyrin had no effect on octanoylated ghrelin level, which was only slightly inhibited by uvaol; the fact that both these triterpenes lack a carboxyl group indicates that this group is important for suppressing octanoylated ghrelin production. These results suggest that triterpenes may have the potential as obesity-preventing agents with suppressive effect on octanoylated ghrelin production.Ghrelin is a 28-amino acid peptide that was isolated from rat stomach (11) and induces body weight gain by increasing food intake (12). Ghrelin exists as two isoforms in vivo: octanoylated ghrelin, which has an octanoyl modification at serine 3, and des-acyl ghrelin without acyl modification (9). Only the former stimulates appetite (13). Suppressing octanoylated ghrelin production is considered as a promising therapeutic strategy for the treatment of obesity. Ghrelin O-acyltransferase (GOAT) catalyzes ghrelin octanoylation (1, 7, 26), and one or more prohormone convertases including furin are required to generate mature ghrelin from the proghrelin precursor (21, 27). We previously established the ghrelin-expressing cell line, AGS-GHRL8, by transfecting AGS human gastric carcinoma cells with the human ghrelin gene (16). AGS-GHRL8 cells expressed both GOAT and furin, and produced octanoylated ghrelin in the presence of octanoic acid (16). We used AGS-GHRL8 cells to develop a cell-based assay system to screen for molecules that inhibit octanoylated ghrelin production (16) and found that fatty acids such as heptanoic acid, stearic acid, linoleic acid, α-linolenic acid and oleic acid decreased octanoylated ghrelin levels (16,17). Since GOAT recognizes fatty acyl-CoA such as octanoyl-, hexanoyl-, and decanoyl-CoA (14), we speculated that the carboxyl group is an important structure for this inhibitory effect.