Stop-flow spectrophotometric method is used to study fast reaction as well as the ternary intermediate complex formation and to determine its stability constant. The stop-flow trace shows the reaction to occur in many steps. The first step is fast, while the later stage is relatively slow. This book is the first report on kinetic study and evaluation of stability constant of ternary complex forming in the MnII - catalysed periodate oxidation of o-Anisidine (OA) and p-Anisidine in acetone-water medium. The formation of ternary intermediate unstable complex during the oxidation of aromatic amines by periodate ion catalysed by MnII has also been proposed in case of some anilines.