The herb Butea monosperma constitutes several human health beneficial components, which are mostly studied for their anticancer effects. In this study, the activity of n-butanol fractions of B. monosperma floral extract was examined on inhibiting aberrant crypt foci (ACF) formation in azoxymethane induced Wistar albino rats. The n-butanol extracts (150 mg/kg) decreased the ACF formation (per rat) by 92%and 78%in short-and long-term in vivo treatments, respectively. All the compounds in the n-butanol extract were isolated and purified using column and reverse-phase high pressure liquid chromatography (HPLC). Their structures were characterized using UV–visible spectroscopy, nuclear magnetic resonance (NMR) and electrospray–ionisation mass spectrometry (ESI–MS) to determine important flavonoids, namely isocoreopsin, butrin and isobutrin. These compounds were studied for their free radical scavenging and anticancer activities. The compound isocoreopsin showed significantly greater efficacy in cell death on human colon and liver cancer cell lines (50μg/mL in HT-29 and 100μg/mL in HepG2) than butrin (100μg/mL in HT-29 and 500μg/mL in HepG2) and isobutrin (80μg/mL in HT-29 and 150μg/mL in HepG2). These results suggest that isocoreopsin, butrin and isobutrin are the important key compounds for the chemoprevention of colon cancer and isocoreopsin can be considered as a promising novel drug.