A table of annual sea state occurrences is prepared based on the significant wave heights and modal periods, two parameters representing a Bretschneider wave spectrum. Measurements of them were done by the Korean Ocean Research and Development Institute (KORDI) at 67points around the Korean peninsula for 22 years. Also the average values of parameters over 4 regions and 4 seasons were derived. Comparative seakeeping calculations using wave parameters prevalent around Korea and those of the North Pacific at sea state numbers 3, 4, and 5 respectively, show some differences in the assessed seakeeping performance.