Alkaline hydrolysis of 2-alkyl-2-oxo-1,3,2-dioxaphosphorinane and -phosphepane was studied in aqueous dioxane. The rate constants were determined at various temperature and the activation parameter of the reaction were evaluated. The hydrolytic process is classified as a AE reaction. Quantitative structure-reactivity relationship was examined by multiple regression analysis involving the rate constants and the structural parameters of the exocyclic substituents on phosphorus. The difference between the hydrolytic behaviour of cyclic alkylphosphonates and carboxylates was also discussed.