The purpose of this study is to investigate the educational philosophy and the happiness principle of Plato and Mencius. To discuss the study systematically, three research questions are stated. First, what is the educational philosophy of Plato and Mencius? Second, what is the happiness principle of Plato and Mencius? Third, what are significant similarities and differences between Plato and Mencius? In order to defend the research questions, a descriptive content analysis method will be utilized with a cross culturally comparative approach. As for the limitations of the study, the principles and aims of education are mainly discussed from a standpoint of educational philosophy. The principles of happiness are also reviewed in the aspect of moral and political theories. This article is mainly focused on the Works of Mencius, and on the Republic of Plato. The author in this article intends to use modern English second resources as well as the classical Chinese and Greek primary languages. Finally, the researcher concludes this study with the suggestion of future research. The significance of the study is to provide the basic theories and worthy resources in contemporary education, especially moral or happiness education, for educational theorists and practitioners in the world in the aspect of the mutual understanding of the Eastern and the Western cultures.