The pursuit of early diagnostic biomarker and ideal therapeutic target for prostate cancer has never been stopped. So far, a number of proteins have emerged as potential clinical candidates in the treatment. One of most important novel biomarker is prostate stem cell antigen (PSCA). PSCA is a glycosylphosphatidylinositol (GPI)-anchored cell surface protein that belongs to the LY-6/thy-1 family. It is highly over-expressed in human prostate cancer cells, but is mildly expressed in normal tissues. This restricted expression profile makes it be a potential biomarker of diagnosis and prognosis for prostate cancer, and an attractive candidate target for immunotherapy. Many investigations have revealed that PSCA expression is positively correlated with Gleason score, tumor stage and bone metastasis in prostate cancer. Since PSCA is a prostate cancer-specific membrane antigen and has restricted pattern of expression, it has been targeted in several immunotherapeutic strategies, including monoclonal antibodies, antibodies conjugated to cytotoxins, genetically engineered T cells, PSCA vaccination and peptide-loaded dendritic cells (DC). This article presents the currents progress of PSCA in the diagnosis, prognosis and therapy for prostate cancer, and provides a general introduction of some different findings about its expression in other cancers