Carbon ion radiotherapy (CIT) shows encouraging results in the treatment cancers, including those resistant to conventional photon therapy. National Institute of Radiological Sciences (NIRS) in Japan and Heidelberg University Hospital in Germany have been the pioneers in the development of carbon ion therapy since the 90’s. In 2006, a compact accelerator system for CIT was built at the Gunma University Heavy Ion Medical Center (GHMC), which marks the turning point of increasingly worldwide spread of this state-of-the-art therapy. Accumulating research and clinical data is facilitating our understanding in the biological features of CIT effects and their potential impacts on the outcomes of cancer treatment. In this presentation, current clinical results of CIT treatments for various cancer types will be discussed. Additionally, hypoxic tumor microenvironment, DNA repair for double-strand breaks, radiation-induced apoptosis as well as some CIT preclinical data will be outlined.