It is intended to provide a chromium (III)-containing aqueous solution which has widely adjustable molar ratios of various acid radicals to Cr and is useful as a source of trivalent chromium or a supplementary source of trivalent chromium for the bath in the surface treatment of various metals. Specifically, the chromium (III)-containing aqueous solution is characterized by containing a complex chromium (III) salt which is produced by performing chromic acid reduction reaction in the simultaneous or sequential presence of two or more acids selected from an inorganic acid other than chromic acid and an organic acid. Furthermore, it is intended to provide a process for producing a chromium (III)-containing aqueous solution by performing chromic acid reduction reaction by the contact of chromic acid with an acid other than chromic acid and/or an organic reducing agent in a water solvent, characterized in that the chromic acid reduction reaction is performed in the simultaneous or sequential presence of at least two or more acids selected as the acid other than chromic acid from an inorganic acid and an organic acid.