Inhibition of PI3K/Akt pathway might be the best way to overcome colon cancer and small molecules [e.g., 2-(4-morpholinyl)-8-phenyl-chromone (LY294002)] are being developed for cancer therapy. Recent studies revealed that 3,3-diindolylmethane (DIM) has antitumor effects both in vivo and in vitro models of colon cancer. Therefore, this study aims to investigate the antitumor effects of DIM plus LY294002 in human colon carcinoma cancer cells. Two human colon cancer cell lines (HCT-116, HT-29) were used to test the response to DIM plus LY294002. MTT assay, flow cytometry, and western blotting were conducted. DIM plus LY294002 significantly inhibited the proliferation of human colon cancer cells in a dose dependent manner compared to when DIM or LY294002 is treated alone. The percentages of cells in the G1 phase were significantly increased 12h after being treated with DIM plus LY294002. DIM plus LY294002 significantly induced cleaved poly (ADP-ribose) polymerase and cleaved caspase9 levels. In addition, DIM plus LY294002 significantly induced p-YAP and suppressed YAP expression. Therefore, these results suggest that DIM may have more dramatic therapeutic effects when it is combined with PI3K inhibitors in the treatment of colon cancer cells.