Recently, researches on the reduction of the pitching motion of ships are actively pursued. The anti-pitching tank and anti-pitching fin etc. may be cited as examples. This paper presents the effect of activated anti-pitching fins upon pitch reduction. The attack angle of the fins can be varried by signals of K ₁ψ+ K ₂ψ+ K ₃ψ, where ψ is pitching angle and K ₁, K ₂ and K ₃ are constant. According to the theory which was introduced in this paper, it is desirable to take a combination, K ₁ >0, K ₂> 0 and K ₃ < 0, in order to reduce the maximum amplitude of the frequency response. But from the viewpoint of comfort of passengers in ships, it is suitable to take a conbination, K ₁ <0, K ₂ >0 and K ₃> 0. And it is expected from the calculation that the maximum pitch amplitude of a ship with controlled fins is about 50% lower than a ship's with fixed fins, and 60% lower than a ship's without fins. On the other hand, an experimental study has been conducted in regular waves using pitching angle and it's angular velocity as signals to move fins. And the results of the experiments showed that more than 80% pitch reduction can be obtained, and that anti-pitching fins are also very effective for heave reduction.