Worldwide, cervical cancer (CC) is the third most common malignancy in women, and it remains a leading cause of cancer-related death of women. Genomic studies indicate that phosphoinositide 3-kinase (PI3K)/AKT signaling is one of the most frequently deregulated pathways in several human cancers, including CC. This signaling pathway has an important role in cancer cell proliferation, survival, motility, and metabolism, and therefore could be an attractive therapeutic target. In a previous study, we used a sensitive and high-speed homogeneous assay for the detection of kinase activity and for screening of PI3K/AKT signaling inhibitors in a high-throughput screening (HTS) format and then obtain formononetin, as an O-methylated isoflavone existed in a number of plants and herbs like Astragalus membranaceus. We showed that formononetin inhibited the phosphorylation of AKT and induced the apoptosis of CC cell line HeLa in a dose-dependent manner. Furthermore, formononetin suppressed xenograft tumor growth in nude mice. Our results indicated that formononetin may be used as an anti-cancer drug for cervical cancer in the future.