Performance of a hydrofoil sailing boat equipped with two surface-piercing dihedral foils and an inverted “T” foil has already been analyzed in the previous paper. The estimated sailing performance in terms of a static balance calculation agreed reasonably well with results of sea test using a boat of 5.08m LOA. In the present investigation, dynamic performance and stability of the boat are examined as an extension of the previous work. The equilibrium state for the sailing is determined by solving six simultaneous non-linear equations as a function of wind velocity, wind direction and the angle between the boom and boat centerline, which is called sail trim angle. Then the dynamic stability around equilibrium state is examined on the basis of linear theory for small disturbances by assuming a constant heading angle against the true wind direction. Finally motions around the equilibrium state is computed by numerical simulation to compare with the results of stability analysis. The sailing performance of the boat is affected by sail trim angle. The smaller the angle, the higher become the boat speed with the less stability in the sailing state and vice versa . The stable sailing become difficult with increasing the wind velocity. These analysis for the dynamic stability agree well with the results of the numerical simulation.