Abstract: This apaer paper presents a method for estimating the added stiffiness and mass on a structure so that the dynamic response of the structure to harmnonic excitation can meet the predetermined requirements. The analysis is made through generalized inverse theory with the use of modal data. The general exprssions of the added mass and shffness parameters are derived. This method uses only the dynamic flexibility data on the degrees of freedom associated with the modifying parameters, therefore, it is simple in computation and experimentation Numerical examgles are given to show the effectiveness of the proposed method.