The unusual hypolipidemic activity of the methanolic fractionate of the essential oil (EOM) obtained from the mountain celery seed was previously reported. The most enriched 9(Z)-octadecenamide (oleamide) was speculated to be responsible for the relevant bioactivity. Chemically syntheized oleamide (CSO) yielded 85.1% with a purity of 98.6% when identified by RP-HPLC, FTIR, HREIMS, (1)H NMR, and (13)C NMR. CSO was tested for its antioxidative and hypolipidemic bioactivities. Results indicated CSO was potently hypolipidemic with regard to serum TG, TC, LDL-C, LDL-C/HDL-C, and hepatic TG (p < 0.05), but not for serum HDL-C and hepatic TC. In addition, CSO exhibited only poor antioxidative activity, implicating the possibility that the hypolipidemic and antioxidative bioactivity of original EOM was due to another coexisting constituent, probably gamma-selinene. Conclusively, oleamide is a potent hypolipidemic agent as regarding its effects on decreasing serum TG, TC, LDL-C and hepatic TG.