Genistein, is one component of soy which showed to contribute in cancer chemoprevention mechanism by modulating the phase II metabolism enzymes In Vivo. Uridine diphosphoglucuronosyltransferase1A8 (UGT1A8) is an extra-hepatic UGT1A family, expressed in the lower GIT and is responsible for the phase II metabolism of drugs, xenobiotics and by-products of endogenous metabolism. This study investigated the role of genistein in regulating UGT1A8 gene expression and the mechanism that may involved. The Caco-2 cell line was used to induce a small intestine enterocyte-like phenotype by either a long or short-term differentiation protocol. The short protocol uses sodium butyrate (NaB), a known histone acetylation regulator and by product of fibre fermentation. Caco-2 cells carrying an integrated 7kb UGT1A8 promoter segment linked to the luciferase reporter were used to assay the effect. We transiently transfected 7kb and 1 kb UGT1A8 promoter constructs in Caco-2 cells to identify transcription factors that may mediate UGT1A8 regulation downstream of genistein. Our results showed that genistein functioned synergistically with NaB in differentiated Caco-2 cells to induce UGT1A8 promoter activity more than 18 fold. Consistent with this, the same treatment increased the UGT1A8 mRNA, suggesting an activation mechanism which involves histone hyperacetylation. Genistein is known to function through estrogen receptors (ERs) and peroxisome proliferator activated receptors (PPARs). Treatment with ER agonist 17-β estradiol did not activate UGT1A8 expression and blocking with the antagonist ICI-182780 did not inhibit genistein action. In contrast, the PPARγ antagonist GW9662 attenuated the activating effect of genistein and butyrate on the UGT1A8 promoter. Consistent with this, UGT1A8 expression was increased by PPARγ agonist Rosiglitazone. These results provide evidence on the role of genistein in regulating UGT1A8 in the presence of NaB by involving the PPARγ pathway. It is possible that soy consumption in conjunction with a high-fibre diet may mediate protection of the GIT from carcinogens by induction of UGT1A8.