The photochemical reaction of dichromated gelatin solution in the spectrally sensitized region was investigated under normal room conditions employing a water-soluble gelatin. Sample solutions containing dichromate, gelatin, methylene blue (MB) and pH buffer solution, were exposed with the light limited to longer wavelength than the intrinsic sensitive region of dichromate. The decrease in absorbance for the photoreduction of Cr(VI) was monitored by UV-visible spectroscopy. For comparison, ethylenediamineacetic acid (EDTA) was used as a reducing agent. It found that the reaction order, pH dependence of reaction rate, and activation energy differed both when gelatin and EDTA were compared. On the basis of experimental observations and discussion, a mechanism and its rate determining step were proposed.