In this study, three model compounds of urea-formaldehyde resin, such as methylene diurea, Uron and tetrahydro-5-ethyl-2(1)-s-triazone, were synthesized. The rate of hydrolysis in pH 4.0 buffer solution at 80℃ was measured with iodimetric method. The result showed that the stability orderof the model compounds in acid condition was Uron>methyene diurea>tetrahydro-5-ethyl-2(1)-s-triazone.