Available data on statistics of wave height and period have been collected on the world sea areas and routes. The purpose of this paper is to establish tentatively standard family of wave spectra for prediction of wave bending moments in rough seas based on such wave data. Theoretical wave spectra originally proposed byNeumann, Darbyshire, Roll-Fischer and Pierson-Moskowitz were modified realistically to fit the observed sea states and compared with each other. Further, the comparative investigation was carried out on the standard deviations of wave bending moments of two ships in rough seas, which were obtained from those wave spectra and response operators. There are not so significant differences between the results obtained from those modified wave spectra. The results derived from modified Darbyshire spectra, however, have a tendency rather different from the others. Modified Pierson-Moskowitz wave spectra proposed by I. S. S. C. would be appropriate for short-term and long-term pridiction of wave bending moments in rough seas and acceptable as an interim proposal.