In order to estimate stability limit of the maneuverability of ship in following sea, an analytical method combining simplified potential flow theory and Froude-Kriloff hypothese is developed to predict the course stability derivatives of ship located in any place of regular waves. Comparison between the values calculated by this method and these obtained from experiment has been carried out. Calculated magnitudes are more or less different from experimental results, but they show quite good tendencies from the view point of the physical phenomena.