Morphology and internal structure of monodispersed pseudocubic hematite (alpha-Fe2O3) particles produced by the gel-sol method were investigated in detail through high-resolution electron microscopy on their thin sections prepared with an ultramicrotome. It was confirmed that the c-axis of a particle corresponded to the longest diagonal axis of the particle. High-resolution electron micrographs of thin sections directly revealed the polycrystallinity of the particles and clearly showed the arrangement of the subcrystals and their crystallographic orientations. The subcrystals near the surface of a particle were of a rectangular shape bound by the {<01(1)over bar 2>} planes, and their width was about 12-16 mn with small variation of the length depending on the position in a particle. The subcrystals were radially developed from the center of a particle in all directions, but most preferentially in the longest diagonal axis of a particle. Besides, it was found from EDX analysis that the adsorbed Cl- ions as a shape controller were incorporated into the pseudocubic hematite particles during their growth.