The Beijing electron-positron collider and its second phase construction

As a powerful tool for research on the micro-world, colliders have played an essential role in the exciting discovery of particle physics in the past 30 years, and continue to serve as the dominant machines for high energy physics research. Aiming at τ and charm physics, the Beijing Electron-Positron Collider (BEPC) has become a leading machine in the world in its energy region. Many important results in high energy physics and synchrotron radiation research have been obtained with the BEPC. To maintain China's leading positron in τ and charm physics, Chinese scientists proposed the BEPCII project as the second phase construction, and this was approved by the Chinese government at the end of 2003. As with the BEPC, BEPCII will serve two purposes, i.e. research on high energy physics and synchrotron radiation. The luminosity of BEPCII will be two orders of magnitude higher than the present BEPC, and its synchrotron radiation operation will also be significantly improved. The performance of BEPC and progress in the construction of BEPCII as well as their prospects are reviewed.