Ganoderma sinense or “Chinese Lingzhi” is a well-known medicinal fungus in China for more than 2000 years. Polysaccharide is the main immunomodulatory and antitumor component in G. sinense. In 2010, G. sinense polysaccharide (GSP) tablet is approved as an adjunctive therapeutic drug in China for treating leukopenia and hematopoietic injury caused by concurrent chemo/radiation therapy during cancer treatment by the State Food and Drug Administration (SFDA). β-glucan, an established immunostimulant, is one of the components in GSP. Based on CNKI (China National Knowledge Infrastructure), VIP (Chongqing VIP Chinese Scientific Journals Database), Wanfang database, and PubMed searches, we have not only summarized but also translated all the basic and preclinical studies about GSP published in Chinese into English in this review article. Unfortunately, all the clinical studies about GSP tablet could not be found during the search or by contacting the drug manufacturers. However, both basic and preclinical studies showed that GSP has antitumor, antioxidant, anticytopenia, and unique mushroom-poison detoxification properties that are different from that of G. lucidum polysaccharide, another “Lingzhi” polysaccharide. The structure and molecular mechanisms of GSP are also discussed. This article urges availability of clinical study results of GSP tablet that would allow in-depth evaluation if the tablet is appropriate to serve as an immunomodulatory drug during cancer therapy at world stage.