Activation of androgen receptor (AR) stimulates the growth of not only androgen-dependent but also of androgen-refractory prostate cancer. However, neither the role of AR in invasion/metastasis nor the relationship between invasiveness and androgen-refractory status has been established. In this study, we used the androgen-dependent prostate cancer cell line MDA PCa 2b, derived from a human bone metastasis, to generate an invasive subline (MDA-I) using a Matrigel chamber. MDA-I cells expressed higher levels of AR and prostate-specific antigen than their less invasive parental cells. Blocking AR function or removal of androgen suppressed the invasion of MDA-I cells, whereas stimulating AR increased invasion. In addition, forced AR overexpression increased the invasiveness of MDA PCa 2b cells. Next, we showed that an androgen-refractory subline (MDA-hr) of MDA PCa 2b cells also expressed higher levels of AR and were more invasive than their parental androgen-dependent cells. Blocking AR function suppressed the invasiveness of MDA-hr cells. Gelatin zymography indicated that matrix metalloproteinase 2 (MMP-2) and MMP-9 activities were regulated by AR signaling and closely correlated with the invasiveness of the androgen-dependent and androgen-refractory prostate cancer cells. These data suggest that AR promotes the invasiveness of both androgen-dependent and androgen-refractory prostate cancer and that a more invasive phenotype might develop through AR activation during cancer progression. These findings potentially support the use of adjuvant hormonal therapy and the future development of more potent androgen blockade therapy.