As a part of the green process for manufacturing chromium compounds, two steps are involved in the synthesis of ultra-fine Cr2O3 powders: the first is the hydrogen reduction of K2CrO4 into intermediate trivalent (Cr3+) or tetravalent (Cr4+) chromium compounds; the second is the decomposing of the intermediate into Cr2O36 by heat treating. The intermediate is well characterized by means of SEM, XRD, and XPS. The possible reaction mechanism of the process is analyzed.