The reduction reaction of chromic acid by oxalic acid was studied by using a single beam photodiode array (PDA) spectrophotometer. The principal component analysis (PCA) and the target factor analysis (TFA) techniques were applied to handle the spectral data obtained and to determine the absorptivities of the light absorpting species involved as well as the rate constants of the reduction process. The result of computation confirms that an intermediate with an absorption spectrum similar to that of chromium (V) in the spectral range of 476 to 596nm was generated. © 1993, Taylor & Francis Group, LLC. All rights reserved.