70cm long Yb3+-doped Y3Al5O12 (Yb:YAG) single-crystal fibers of 1 and 0.4 mm diameters were grown by the micro-pulling-down method. The structural and optical characterizations of those fibers showed that they exhibited a perfect single crystalline structure and have a homogeneous distribution of the Yb3+ ion in the YAG host. In diode-pumped laser operation, a continuous wave output power of 50 W at 1030 nm was demonstrated for 180 W of pump power at 940 nm, for 1 mm diameter fibers. For 0.4 mm diameter fibers, 28 W at 1030 nm for 100 W of incident pump at 940 nm power was achieved. To the best of our knowledge, these results are the highest laser power ever obtained with directly grown single crystal fibers. (C) 2009 Elsevier B.V. All rights reserved.