We have studied the microstructures of subgrains in large-grain RE123 (RE=Y, Nd, Sm) bulk superconductors through microscopic observation and micro-area x-ray pole figure analyses. We have found that misorientation of the subgrains increases along with the crystal growth, and also that the misorientation has a positive relation to the size and concentration of the second-phase particles. An electron backscatter diffraction technique was successfully utilized for characterizing the subgrain boundaries. We have also performed magnetic and electric measurements for several samples having different subgrain structures. The results of AC transport measurements indicated that the subgrains act as weak links, especially in a high magnetic field region.