ZnIn2S4 is known to be a visible light-active photocatalyst. In this work, it is shown that by substituting part of the In atoms with vanadium, the visible light range of photocatalytic activity of such material can be extended, using the so-called in-gap band scheme that has been shown to enhance photovoltaic characteristics. Characterization of this material using several techniques, complemented by DFT calculations, will support this statement. While here only the degradation of aqueous HCOOH in well-aerated conditions is discussed, the same material may be used, with an adequate sacrificial reagent, for photocatalytic H2 generation.