Measurements of electrical resistivity, X-ray diffraction patterns, magnetic susceptibility and thermoelectric power of the Er1-xPrxBa2CuO7-delta system have been made. The superconducting transition temperature was found to decrease monotonically with praseodymium concentration, x. From the susceptibility data, it was determined that the valence of praseodymium lies between + 3 and + 4. The thermoelectric power was found to increase with x, and the slopes of dS/dT were negative except for the case x = 0. The . tendency of the thermopower to change with increasing praseodymium concentration has been qualitatively explained using the theory for strongly correlated systems.