Title: XMASS Authors: Hiroyuki Sekiya, for the XMASS collaboration
The XMASS detector is a large single phase liquid Xenon scintillator. After its feasibility had been studied using a 100 kg size prototype detector, an 800 kg size detector is being built for dark matter search with the sensitivity of 10^{-45} cm² region in spin-independent cross section. The results of R\&D study for 800 kg detector, especially ultra low background technologies, and the prospects of the experiment are described.