The temperature dependent thermoelectric power and resistivity for a series of disordered (Nd0.8−xPr0.2Cax)Ba2Cu3O7−δ with 0⩽x⩽0.20 has been measured in order to study the disorder effect induced by Pr-doping, in which 50% of the Pr ion is in the Pr(IV) state deduced from unit cell volumes. The hole concentration in CuO2 planes (psh) of the samples has been estimated from the oxygen stoichiometry. Tc-suppression by Pr-doping could not be recovered by increasing psh, demonstrating that the ionic disorder effect plays an important role on Pr-doped samples.