Cancer cells are characterized by an uncontrolled increase in cell proliferation. G1 to S transition is one of the two main checkpoints used by cells to control the cell cycle progress and cell proliferation. G1/S progression is highly regulated by multiple intracellular signaling transduction cascades including Akt and p53 pathways, which therefore becomes a promising target for the development of novel anticancer therapy. Scutellaria barbata D. Don (SB) is a major component in many Chinese medicine formulas that have long been used in China to clinically treat various cancers including colorectal cancer (CRC). Recently, we reported that the ethanol extract of SB (EESB) is able to induce cancer cell apoptosis via activation of the mitochondrion-dependent pathway and inhibit tumor angiogenesis through suppression of Hedgehog signaling. To further elucidate the precise mechanisms of its antitumor activity, in the present study we evaluated the effect of EESB on the proliferation of human colon carcinoma HT-29 cells and investigated the underlying molecular mechanism. We found that EESB could inhibit the proliferation of HT-29 cells through blocking the G1/S cell cycle progression. In addition, EESB treatment profoundly promoted antiproliferative p21 expression, but inhibited the expression of pro-proliferative PCNA, cyclin D1 and CDK4 in HT-29 cells. Moreover, the phosphorylation/activation of Akt was significantly suppressed by EESB treatment, whereas that of p53 was enhanced. These results suggest that EESB could effectively induce G1/S arrest in human colon carcinoma cells via modulation of multiple cell cycle-related signaling pathways.