Rates of reaction and product formation were measured in photodecomposition experiments of aqueous sodium chlorite at 253.7 nm in a reactor that was continuously sparged with nitrogen to remove chlorine dioxide. Rapidly removing chlorine dioxide greatly reduced the formation of chlorate. The results of this work suggest that chlorate is not formed by direct decomposition of chlorite, but rather by decomposition of chlorine dioxide. The results are consistent with the stoichiometry, 3ClO2- + H2O (+hnu) --> Cl- + 2CIO2 + 2OH- + 0.5O2. The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions. Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6. Results of this work provide indirect evidence of the validity of certain elementary steps in mechanisms that have been proposed by previous workers. Quantum yields were measured for both photodecomposition of chlorine dioxide and sodium chlorite. For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.