Research studies of Qigong therapy for cancer for the past 20 years in China were reviewed from three different categories: clinical study on human cancer patients, in-vitro study of cancer cells, and in-vivo study of cancer with Qigong therapy, in an attempt to understand the role Qigong therapy plays in cancer treatment. There is a lot of evidence suggesting that Qigong therapy has an inhibitory effect on cancer growth, both in vitro and in vivo studies, as well as in clinical observation (often there was room for improvement in these studies and some studies require replication in order to verify their findings). Qigong therapy for cancer is an area that is often neglected by mainstream medicine and research, and it should be seriously examined and considered as an important supplement to conventional cancer treatment.