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In this paper, a new Temperature-Sensitive Paint (TSP) technique for boundary-layer transition detection in a production-type large cryogenic wind tunnel is present. The formulation of Ru(trpy) based TSP system has been optimized in terms of luminescence intensity and robustness. The optimum dye-binder-solvent combination has been determined through systematic sample tests. A new hinder has been introduced and the resulting coating was found free from cracking at cryogenic temperatures. This is contrary to the silicone-based pervious cryogenic TSP that are subject to micro cracks at reduced temperatures. The new TSP can meet the root-mean-square roughness requirement less than 0.15 pm. Experiments in the NAL 0.1-m Transonic Cryogenic Wind Tunnel have shown that transition occurs earlier on the unpolished surface than the polished surface, although the roughness value itself increasing by polishing. This suggests that the waviness of the coating could affect on the growth of instability in boundary layers. l "The cryogenic wind tunnel is a vital tool for simulating viscous flow over airplanes at high Reynolds numbers.' To develop high-efficient transports, transition location of boundary layer on model surfaces has to be predicted at flight Reynolds number condition. So far, a technique using an infrared camera has been used for transition detection in a cryogenic wind tunnel However, it is not easy to use this technique in routine tests because it requires a sophisticated IR camera cooled with liquid helium.'In mid 1990's, a new global measurement technique for transition location in a cryogenic wind tunnel was developed under the cooperative program between National Aerospace Laboratoly (NAL) in Japan and Purdue University (USA) ?, 'This technique utilized Temperature-Sensitive Paint (TSP) composed of Ruthenium luminescent molecules and silicone hinder. The luminescence intensity of this paint is highly sensitive to a change in temperature over 90K to 200K. Using this paint, a boundary layer transition over model surfaces can he visualized as thermal signame during a step change in flow temperature.The capability of this technique has been verified in the NAL 0.1-m Transonic Cryogenic Wind Tunnel (NAL 0.1-m TCWT). However, application of the TSP technique to large-scale cryogenic wind tunnels such as European Transonic Windtunnel (ETW) and National Transonic Facility (NTF) is not straightfoward. There are several technical challenges that have to he overcome before bringing this technique to an industrial environment of large cryogenic wind tunnels: 1) High luminescent intensity: Intensity of excitation light varies inversely proportional to the square of the distance between the model and the light source. To apply TSP in large-scale cryogenic wind tunnels, a new TSP formulation that can provide maximum brightness and highest temperature sensitivity has to be developed.2) Coating robustness at cryogenic temperatures In general, polymer coating on a metallic substrate is subject to cracking when exposed to cryog...