Abstract:In the resultant phase of peritectic decomposition of the RE123 (REBa2Cu3O7-δ), RE211(RE2BaCuO5) plays an important role in the construction of RE123 bulk, thin film, and coated conductor. In RE123 bulks, the boundary defects between RE211 particles and RE123 grains serve as strong flux pinning and thus help to increase the critical current density(Jc). In RE123 thin films, the influencing factors of formation of RE211 inclusions are important for obtaining high quality RE123 thin film. In the fabrication of coated conductor, second-phase Y211 particles of nanometer size were introduced by growth of alternating multilayer of ultra thin Y211 and Y123. Such a structure greatly enhances the Jc under a high magnetic field. As RE211 greatly influences the RE123 fabrication and its superconductive property, the growth of RE211 and the growth of large size Sm211 single crystal whiskers are a very important. In this paper, the experimental studies on RE211 single crystal whisker are reviewed, including also large size Sm211 single crystal whiskers(length over 15.5mm) growth by melt-method in single crystal stove.