The weldability of Ni-base single crystal superalloys was investigated by welding CM247LC and CMSX4 samples with characteristic surface orientations with pulsed and CW YAG lasers or TIG arc under various welding conditions. In pulsed welding cracks and different crystals were formed so easily that they could not be avoided. The conditions for prevention of cracks and/or different crystals evolution were established in bead-on-plate welding with CW laser or TIG. Different crystals were formed due to easier heterogeneous nucleation from the vicinity of carbides or intermetallic compounds at the fusion boundary. The evolution of different crystals could be reduced at moderate welding speeds and low powers (heat inputs). The effect of crystallographic surface orientation on the occurrence of different crystals was confirmed and interpreted in terms of different angles between [100] orientations and thermal gradient direction.