Crack-free homogeneous Er/Mg co-doped LiNbO3 single crystal fibers were grown by the micro-pulling down method. The structure as determined from XRD diffraction is hexagonal and lattice constants were a = 5.1570 Angstrom, c = 13.8595 Angstrom and a = 5.1587 Angstrom, c = 13.8578 Angstrom, for 0.6 mol% Er2O3/1 mol% MgO and 0.6 mol% Er2O3/3 mol% MgO co-doped LiNbO3 crystal, respectively. The segregation coefficient of Er3+ ions was in the range of 0.85-0.86 according to the MgO in the starting charge. Also, the transmission spectrum of the crystal was measured and the photoluminescence spectra were observed. (C) 2002 Elsevier Science B.V. All rights reserved.