Abstract: The natural frequency is one of the parameters characterizing the feature of the anti-rolling tank. Based on the comparative research on the commonly used methods of choosing the natural frequency of the controlled passive anti-rolling tank, this paper develops a new method of choosing the natural frequency for the tank, in which selecting the natural frequency of the anti-rolling tank should be based on the range of variation of wave frequency of the sea area in which the ship operates, the range of the ships rolling frequency and the other dependent factors.

Key words: natural frequency, anti-rolling tank, rolling motion