Landscape impact assessment(LIA) is an aid to decision-making. For the decision maker, LIA provides a scientific examination of the predicted landscape implications of a proposed action and of the mitigation measures, before a decision is taken. Thus, the efficacy of LIA depends on the scientific credibility of the prediction and mitigation measures described in the landscape impact statement. The purpose of this paper was to examine the efficacy of LIA through the content analysis of prediction and mitigation measures in the selected 39 landscape impact statements and 34 environmental impact statements. The content of the selected statements was analyzed in terms of the quantification, precision, significance, and likelihood. The results showed that both prediction and mitigation measures were very low in the scientific credibility. Specifically, the prediction was ambiguously described without scientific probability, and the effect of mitigation measures was not specifically presented in the reports. Thus, landscape impact statement can not give credible information in the decision making process, which weakens the efficacy as an aid to decision-making. Based on the results, several suggestions were presented to enhance the efficacy of LIA.