The present paper establishes two equations on gelation reaction of type ∑Aa1-B2
containing two unknown numbers of functional group and weight average functionality. A quadratic equation is obtained by solving the simultaneous equation. Coefficient of the equation
functional group number and weight average functionality indirectly measured. When the method is applied to hydroxyl number determination of HTPB initiated by H2O3
the hydroxyl number is two times as large as one obtained by existing classical acetylizing method.