T. Uchiyama, T. Tomaru, D. Tatsumi, S. Miyoki, M. Ohashi, K. Kuroda, T. Suzuki, A. Yamamoto, T. Shintomi

We are developing a cryogenic mirror suspension for a LCGT project which is a future plan of a km scale laser interferometer of Japan. The suspension consists of a sapphire cylinder as a test mass and sapphire fibers as suspension wires. We have studied the suspension about three points of views that are cooling the test mass, a Q-factor of the test mass and a Q-factor of the sapphire fiber. We will summarizely talk about the suspension with experimentally results.