Abstract So far, nano-sized defects generated by irradiation techniques are the most powerful approach to very strong pinning capability. In the present study, chemical attempts have been alternatively investigated to introduce with a melt texturing process the following different types of nano-sized pinning defects: (a) nano-scale correlation of lattice defects, (b) nano-sized particles or needles of a secondary phase, and (c) extended structures with correlated nano-sized defects. A periodic array of nano-scale twin boundaries has been formed inside melt-processed YBa 2Cu 3O 7− δ (YBCO) with Ru additions. The pinning efficiency of the resulting material is strongly modified in the presence of such disorder. The arrangement of the regular twin boundary along the c-axis has a strong influence on irreversibility line and critical current density. The behavior of the irreversibility line indicates correlated disorder which was attributed to the formation of arrays of nanotwins. The field tilt angle below which pinning by the twin boundary is effective is found to be approximately 40°.