In HTM21 Project we develop Ni-base superalloys with higher temperature capabilities for aerospace and power industories. 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 even higher than CMSX-10. TMS-75 is now being evaluated in private companies inside and outside Japan. Some modifications are also being made by 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 group. ADP and CVM are developed and being used in the alloy development. The location of solute atoms within the structures in the alloys were investigated using atom-probe field inon microscopy(APFIM) and compared with predictions by ADP and CVM.