The morphologies of (001) gamma/gamma' interfacial dislocation networks are studied through TEM observations. The lattice misfit has an important relation with creep property for superalloy during high temperature creep deformation. The fourth generation superalloy TMS-138 possesses superior creep properties based on its fine interfacial dislocation networks. The networks have two typical characteristics: closely spaced dislocations and stable square morphology during creep deformation. Such arranged dislocations can effectively prevent the slipping dislocations in the gamma phase from moving through the gamma/gamma' interface and improve drastically the creep resistance in the fourth generation superalloy TMS-138. (C) 2003 Kluwer Academic Publishers.