Single crystals of YBa2Cu3Ox superconductor were grown by means of the flux method. The effectof starting material, cooling rate, melting time, and melting temperjature were evaluated as influencing paraemters. The larger single crystals of YBa2Cu3Ox were obtained with Y2BaCuOy powder as a starting material than with YBa2Cu3Ox powder. The optimum range of synthetic condition for single crystal growth was as follows ; 2-5$^{circ}C$/hour of cooling rate, 2-5 hour of melting time and melting temperature at 106$0^{circ}C$. The obtained size of single crystal was 2mm in average and the largest one was 5mm in maximum.