In HTM21 Project we develop Ni-base superalloys with superior temperature capabilities for aerospace and power generation. A 3rd generation single crystal (SC) superalloy TMS-75, which contains 5wt% Re, shows excellent properties; easy heat treatment, stable microstructure, and high creep strength comparable with or higher than CMSX-10. TMS-75 is now being evaluated in private companies inside and outside Japan. Some modifications are also being made using ADP(Alloy Design Program) and CVM(Cluster Variation Method) toward the 4th generation SC superalloys. Light(density=8.0-8.2) SC superalloys, high Cr containg SC superalloys and 3rd generation DS superalloy, TMD-103, are also designed and tested in this research group. ADP and CVM are developed and being used in the alloy development. The location of solute atoms within the structure of the alloys have been investigated using atom-probe field ion microscopy(APFIM) and were compared with the predictions made by ADP and CVM.