Cnidium monnieri (L.) Cusson is an annual plant distributed in China and Korea. The fruit of C. monnieri is used as a medicinal herb and is effective for the treatment of carbuncle and pain in the female genitalia. In this study, we investigated the effects on apoptosis and cell cycle arrest by ethanol extracts from C. monnieri (CME) in HT-29 colon cancer cells. The results of MTT and LDH assays demonstrated the antiproliferative and cytotoxic effects of CME. Also, the number of apoptotic bodies and the apoptotic rate were increased by CME. Moreover, cell cycle arrest occurred in the G1 phase by CME. Akt down-regulates various proteins, such as TSC2 and GSK-3β. Transcription of the cyclooxygenase-2 (COX-2) gene is regulated by the GSK-3β/β-catenin signaling pathway. Overexpression of COX-2 induces production of the anti-apoptotic protein, Bcl-2. To confirm the regulatory effect on signaling proteins of CME, we used Western blot analysis in vivo and in vitro. The results showed that, the expression levels of p-Akt, p-TSC2, p-mTOR, p-GSK-3β, β-catenin, COX-2, Bcl-2 family members, and caspase-3 were regulated by CME. Treatment with specific inhibitors showed that CMEinduced apoptosis occurred through regulation of COX-2 expression via both the Akt/GSK-3β/mTOR and Akt/GSK-3β/β-catenin signaling pathways.