Rotational degrees of freedom (RDOFs) have difficulty with measurement, although structural modifications with beam and plate elements require mode shapes including RDOFs. This paper presents a method to estimate RDOF components as a linear combination of mode shapes of the finite-element (FE) model of a test structure. Since the estimation accuracy depends on a set of combined modes, an effective technique for selecting modes to be combined is proposed. This technique is based on the modal assurance criterion (MAC) value which indicates the degree of correlation between experimental mode shapes having only translational degrees of freedom and analytical mode shapes of the FE model. To demonstrate the applicability of the proposed technique, a frame model which has simulated experimental mode shapes with added measurement noise is analyzed. It is confirmed that the optimal set of combined modes can be predicted from the MAC values, although the set differs with each mode number to be estimated.