It is of importance to design a ship which has a good seakeeping performance in her sea-lane. It is, however, hard to say that an optimization of the hull form for seakeeping performance has been sufficiently carried out from the seakeeping point of view at the initial design stage of a merchant ship so far, because it has been difficult to make clear the seakeeping criteria and the correlation between the hull forms and the seakeeping qualities.In this paper the author derives the regression equation to estimate the correlation between the hull forms and the seakeeping qualities by applying the Bales' procedure to the container ships. He provides the guidelines to optimize the hull form for the seakeeping performance and the added resistance in irregular waves. The calculation is made to determine the hull forms in accordance with the above guidelines, and finally the optimized hull form is shown for the seakeeping performance and the added resistance. It is concluded that the present method is very easy and useful in the early stage of ship design for determining the dimensions of a new ship which has a good seakeeping performance and a small added resistance.