In this paper, the authors carried out model tests to estimate directional wave spectra from only a set of simultaneous records of ship motions. Based on the assumption of linearity between the waves and the ship motions, many studies which estimate the wave power spectra by using only data of ship motions have been done. However, there are few results for estimation of directional wave spectra based on only information of ship motions. The estimating calculation in this paper consists of three steps. The first step is a calculation of cross spectra of ship motions by a stochastic approach using a multidimensional auto regressive model. The second one is a theoretical calculation of frequency response functions of the ship from the waves by New Strip Method. And, the last one is an estimation of directional wave spectra by using Bayesian Model. In order to discuss the quantitative accuracy of this method, some results were compared with the ones estimated from the observing data in an array of wave height sensors. Successful agreement between measured and estimated directional wave spectra was obtained. And the power spectra which were obtained by integration of the estimated directional wave spectra also agreed quantitatively with the measured ones.