The construction of an offshore demonstration wind farm was planned in a southwestern sea-area of the Korean Peninsula. To estimate economic feasibility and to establish a reliable design basis, it is necessary to identify the design parameters of the demo-farm. For a reliable estimation of the design parameters, the first offshore meteorological mast, HeMOSU (Herald of the Meteorological and Oceanographic Special Research Unit), was constructed at the site of the demo-farm. In addition, supplementary meteorological masts were installed in advance at Gochang and Wangdeung-do in order to enhance the estimation of the long-term wind potential for the demo-farm. In this paper, assessments of wind energy potential are carried out with the data measured from these three meteorological masts. The analysis includes seasonal and diurnal changes in wind speed and surface roughness as well as wind/energy rose. Long-term wind potential is also estimated by using MCP (Measure-Correlate-Predict) techniques to clarify the design basis and to determine the wind turbine class in accordance with IEC 61400. The AEP (Annual Energy Production), as well as the C.F. (Capacity Factor) of the candidate site are evaluated with the estimated design parameters. Crown Copyright (c) 2012 Published by Elsevier Ltd. All rights reserved.