Participatory impact assessment is necessary when the uncertainty of the project's future impact is high and complex stakeholder interactions exist. This study examines group model building (GMB) as an applicable method of participatory impact assessment. As a pilot application, a GMB workshop was conducted to assess the impact of offshore wind farm construction projects in local areas of South Korea. Researchers and practitioners participated in the workshop and performed small group activities designed according to the GMB scripts. The results of the workshop showed that GMB's activity of building a causal loop diagram could contribute to assessing the uncertain impact and address complex interests by integrating diverse knowledge and perspectives on the future impact of offshore wind farms. Through reflection on the workshop experience, the authors discuss the feasibility of using the GMB workshop as a participatory impact assessment method.