The kinetics of catalytic and non-catalytic hydrolysis of cis-epoxysuccinic acid (H(2)E) to tartaric acid (H2T) have been studied. The hydrolysis proceeded much faster in the presence of sodium tungstate catalyst than with an acid or without any catalyst. The results indicated the formation of complexes {cat.H(2)E} between sodium tungstate (cat) and cis-epoxysuccinic acid, presumably in the form of tunstenglycolate of tartaric acid. The reaction has been found to be retarded by tartaric acid or, rather, by its complex with catalyst in the form {cat.2H(2)T}. A mathematical model of the overall process has been developed and the mechanism of reaction discussed.