In this work, α-Fe2O3 oblique and truncated nanocubes were synthesized in the presence of oleylamine (OAm), acetylacetone (Hacac) and oleic acid (OA) through a facile one-step solvothermal method. The phase of iron oxide was precisely regulated through the volume ratio of OAm/Hacac, and confirmed by X-ray diffraction (XRD) and Raman imaging microscopy. The formation mechanism of α-Fe2O3 nanocrystals was discussed systematically and a schematic illustration of the probable formation of the morphologies in the whole of the synthetic process was also proposed. Furthermore, the truncated nanocubes exposing both the {012} and {104} dominant planes exhibit higher photocatalytic activity toward RhB compared with the oblique nanocubes surrounded by only the {012} dominant facet, which reveals that the high photocatalytic activity is attributed to the exposure of {104} high-index planes. The truncated nanocubes with high catalytic activity may potentially serve as effective and cheap catalysts for photodegradation.