A method for estimating the Doppler coefficient by applying a dynamics identification method from to low power transient test data of FBR Monju has been developed. For dynamics identification, a kinetic simulation code was introduced to reproduce the observed low power transient numerically. This simulation code contains two unknown reactivity feedback coefficients (Doppler coefficient and moderator temperature coefficient) relevant to reactivity feedback due to temperature variations of fuel and moderator (coolant). In the dynamic identification method, these unknown coefficients are determined so as to reproduce the low power transient in the digital simulation using the kinetic simulation code. Numerical analysis shows that reactivity feedback coefficients can be determined from low power transient data of MONJU and estimation errors of feedback coefficients caused by some uncertainties of various parameters contained in the kinetics simulation code are modestly small.