Drinking aqueous celery extract for 8 weeks caused a significant reduction in serum total cholesterol (TC) level in growing genetically hypercholesterolaemic (RICO) rats. In addition, administration of butanol fraction (Fbu) and aqueous fraction (Faq) of celery extract for 7 days by intraperitoneal (i.p.) infusion effectively decreased the serum TC and high-density lipoprotein cholesterol (HDL-C) levels of adult RICO rats. The 8-week study showed that oral intake of celery extract could enhance the 14C-cholesterol/metabolites excretion. The liver and small intestinal sterol synthesis were not affected. Also, long term drinking of aqueous celery extract did not lead to any undesirable side effects on liver functions. The Fbu and Faq lowered serum TC level mainly through increased bile acid excretion but not by modulating the activity of the rate-limiting enzyme for cholesterol biosynthesis, HMG-CoA reductase. Hence, the mechanism elucidated supports that suggested by the 8-week study. A preliminary chemical characterisation of Fbu and Faq fractions by thin layer chromatography (TLC) showed the presence of sugars and amino acids. There is a possibility that polar compounds with sugar or amino acid side chains(s) could contribute to the hypocholesterolaemic action of celery extract.