The rare-earth copper oxide superconductors of Nd1Ba 2Cu3O7-δ, Nd0.5Gd 0.5Ba2Cu3O7-δ and Nd 0.33Eu0.33Gd0.33Ba2Cu 3O7-δ have successfully been synthesized by introducing a wet-mixing method. Sintering was carried out at varying temperatures of 920, 940, 960 and 970°C for 10 hours in air. The effects of sintering temperature on the structural and crystallinity of the synthesized powders was studied using X-ray diffraction techniques. Rietveld analyses gave clearly separated diffraction (013) and (110) peaks at respectively 32.2° and 32.5°, decreasing Goodness-of-Fit, increasing average crystal size and increasing orthorhombicity with increasing sintering temperature from 920 to 970°C. In this research, the superconducting critical temperatures of Nd0.5Gd0.5Ba2Cu3O 7-δ and Nd0.33Eu0.33Gd 0.33Ba2Cu3O7-δ powders sintered at 970°C and measured using a SQUID magnetometer was obtained to be about 88-91 K.