Formononetin (FT) is a natural phytoestrogen isolated from red clover (Trifolium pratense L.). Growing evidences indicate that FT-mediated cell arrest in cancers in vitro. However, detailed investigations on colorectal cancer by FT remain limited. In this study, we aimed to explore the potential benefits of FT and discuss the underlying mechanisms. FT-administered human colorectal cancer cells (RKO cell line) were subjected to testing the changes of endogenous expressions of gene/protein regulators. Prepared RKO tumor-bearing nude mice were used to evaluate the target signal pathway mediated by FT treatment. Compared to the vehicle control, FT inhibited RKO cell proliferation and induced apoptosis. Meanwhile, FT up-regulated the Bax mRNA expression, while lowered Bcl-2 protein expression and ERK1/2 phosphorylated level. In addition, FT lowered serum concentrations of IL-6, PGD2 in tumor-bearing nude mice. inhibited solid tumor growth in nude mouse through decreasing neoplastic TNF-alpha and NF-kappa B productions. Our results demonstrate that FT induces apoptosis in human colorectal cancer cells, which the molecular mechanisms are involved in modulating Bax/Bcl-2 activities and inactivating ERK pathway associated with cell proliferation, as well as inhibiting TNF-alpha/NF-kappa B pathway for controlling cell growth. (C) 2015 Elsevier Ltd. All rights reserved.