There have been no specific health claims for functional foods. So, a lot of namely functional foods have been produced, and consumers confuse these functional foods with conventional foods. Last year, the Chonbuk National University Hospital established a clinical trial center for functional foods to meet the social needs for the validation of functional foods. For a successful clinical trial for functional foods, their characteristics should be understood. The followings should be considered before clinical trial: ① The clinical trial for functional foods is different from that for pharmaceuticals, since the subjects for the functional foods should be healthy and sub-healthy persons, not patients. ② Some clinical trials for functional foods should be done in a larger pool of subjects because functional foods show less significant effects compared to medical agents. ③ The diet should be more tightly regulated for clinical trial of functional foods. ④ Appropriate biomarkers are required for clinical trials for functional foods.