The effect of chemical composition substitutions on the flux pinning and physical properties of (Y,Nd) 1+xBa 2-xCu 3O 7-δ superconductors was studied in powders processed by solid-state reaction and equilibrated in air at 910°C. The powders were subsequently processed in 1% O 2 atmosphere at < 920°C to increase the superconducting transition temperature (T c) and critical current density (J c). After processing in air, the powders were nearly pure single-phase compositions as determined by X-ray diffraction. Powders were finally annealed in 100% O 2 atmosphere at temperatures < 500°C to maximize T c. The T cs of the powders were measured by ac susceptibility and dc magnetization methods. Annealing powders with a final step in 1% O 2 atmosphere compared to processing in air significantly enhanced T c from 65-90 K to > 92 K for all compositions tested, and also increased J c from about ∼10 3-10 5 A/cm 2 to ∼10 6 A/cm 2. The flux pinning properties varied depending on exact composition, and the intrinsic behaviors changed with the final 1% O 2 annealing treatment.