Abstract: A response curve fitting method is developed to estimate parameters of beam-type members with unknown rotational response. Using a set of orthogonal base functions, the translational response curve is firstly obtained by curve fitting. The rotational response curve is then derived by the differentiation of translational curve with respect to the coordinates of measurement points. In order to deal with error propagation problem in curve fitting, a sample-averaging method is introduced which uses the average values of subsets of total sampling set in parameter estimation procedure. Numerical example shows that the rotational response can be obtained accurately by curve fitting method, and the sample-averaging method can reduce the effect of error propagation in parameter estimation.