The structure of dense (99%) high-pressure (2-5 GPa)-high-temperature treated single-phase and melt-textured YBaCuO and NdBaCuO ceramics has been investigated. High-pressure-high-temperature (HP-HT) treatment under 5 GPa in contact with annealed zirconia allows us to prevent oxygen losses from Nd123 and Y123 structures even when heated up to 1100 and , respectively, and thus, keep the superconductive characteristics. For MT-YBaCuO ceramics, a more than twofold decrease in the anisotropy of critical current density occurs because of doubling critical current density in the direction of the c-axis of Y123 crystallites (in the perpendicular direction it remains almost unchanged) may be explained by the increase in dislocation density in the (001) plane (from up to ) and by narrowing of twin domains (from 150 down to 20 nm). For MT-NdBaCuO, narrowing of spacing between the twins has been observed in the polarized optical microscope.