This study purports to investigate theoretically an integrated curriculum for better research and application, and to suggest its development directions. Related to the purpose of the study, first of all, I categorize the current agendas of integrated curriculum research as four phases, including the structure and integration of knowledge, inter-connections among subjects and integral teaching, breadth and depth of knowledge, and developmental sequence of learning contents. Secondly, the researcher inquires the approach of integrated curriculum, focusing on logical and psychological structure of learning contents, broad-curriculum and core-centered integration, concept-, process-, and theme-based learning activities. On the third, the barriers of integrated curriculum have been discussed as follows: a) problems derived from structure or formality of knowledge, b) academic-oriented thought scheme of subject matter experts, c) subject-focused thinking paradigm and instructional method of teachers, d) evaluation system by divisional subject knowledge. Furthermore, solutions and interventions for the problems mentioned above would be suggested. If education is to realize self-actualization of individual students and socially-respected values, the completion of it would be based on humanistic attributes with integrity and socially-desired directions. Since an integrated curriculum is a link in a chain of inquiry for the education, further research, on-site application, and verification of the effects should be elaborated more.