3,3'- diindolylmethane (DIM) is an acid -derived compound formed during the digestion of indole-3-carbinol (I3C), which is one of the main compounds in cruciferous vegetables, such as broccoli, cabbage and kale. Studies indicate that the cancer protective effects of cruciferous vegetables and I3C partially rely on DIM, which is the bioactive form of I3C in the body, and DIM has been shown to interact with several signaling pathways in cancer. However, the primary molecular working mechanism of DIM is still not clear. In this dissertation, we hypothesize that DIM works through estrogen receptor (ER) signaling to inhibit prostate cancer. We focus on DIM's interaction with ER, as well as its effects on preventing advanced prostate cancer and weight gain in the TRansgenic Adenocarcinoma of Mouse Prostate (TRAMP) model.