Since 1960's, Systems Theory marks the fourth stage of Educational Administration Theories following Scientific Management Theory (-1930), Human Relations Approach(1930-50), and Behavioral Approach(l950-). Generally, Systems Theory has been recognized as an effective tool of logical educational problem-Solving way which is applied to identifying and resolving important educational problems. But, the basic concepts of Systems Theory-System, Systems Approach, and Systems Analysis-often have been used exchangeably and ambiguously without defining these concepts precisely among the educators and educational administrators. Therefore, the purpose of this study is to establish the basic concepts of Systems Theory- System, Systems Approach, and Systems .Analysis -, and their relationships by reviewing and analyzing Scholars' definitions about these concepts appeared in domestic and foreign educational administration literatures. As results of scholars' definition analysis of these concepts, the definitions of these concepts are summed up as follows : ① System is a reality having totality or integration which is consisted of Subsystems carrying out purposeful actions to achieve its common goal. ② Systems Approach is a method, tool, way of thought, process, and viewpoint of problem solving, decision making goal attaining, and Systems managing by reasonable, scientific and logical thinking. ③ Systems Analysis is a scientific, Systematic, efficient technique and process to accomplish System's goal (objective) and its problem-solving including quantitative, qualitative and mixed methods. Based on the results of scholars' definition analysis, the present researcher defined the concepts of System. Systems Approach, Systems Analysis as follows: ① System is a total reality of its parts(elements) Which is inter and intra dependent carrying out functions independently toward common goal in a set of rules. ② Systems Approach is a reseasonale way of thought by scientific, Systematic methods and procedures to achieve the System's goal by effective-solving methods. ③ Systems Analysis is a scintific, efficient problem-solving process and technique to manage System by using Systematic, reasonable methods and procedures. Therefore, System is the object or reality of Systems Approach, Systems Analysis as a startpoint, and Systems Approach is a way of thought and a process to understand System and to solve its problems. Finaly, Systems Analysis is a Specific problem-solving process and technique to achieve the System's goal. As a result of this researcher's definitions about the concepts of System, Systems Approach, Systems Analysis, and their interrelationship, this research established the conceptual models concerning to System, Systems Approach, Systems Analysis, and their interrelationship.