Single crystal growing of YBCO superconductor was attempted using a BaO-CuO flux method. 123 superconducting powders mixed with 28 BaCO₃-72 CuO flux in variable compositions were held at 1030℃ for 10 hours and cooled at the rate of 5∼30℃/hr. In the proper composition of melt and cooling rate, YBCO single crystals with the mean size of 1.5 × 1. 5 × 0.1㎣ could be obtained and had grown on the wall of crucible up to the size of 2.5 × 3 × 0.1㎣. YBCO single crystals had a shape of very thin plate with well developed (001) crystal face and were characterized by EDS, XRD, and Laue method.