In this study, after establishing assessment framework and reviewing the conceptual evolution and component of EL(Environmental Literacy) through literature review, through middle school students as population, the level of EL and relationship of its related variables were examined. The investigation was consisted of second and third grades of urban and rural middle schools in Choongbook. The used measurement methods were objective evaluation and Likert-type scale. The questionnaire instrument variables were consisted of 80 items on environmental literacy variables and six items on student gender, area of residence, environmental lesson, degree of environmental concern, environmental information, environmental activity as background variables. The major findings of this study were as follows: 1. Although the broad and obscure concept of EL has been evolved until 1992, it has been developed more systematic and precise after 1992. But there is not still an agreed concept. 2. The subordinate components of EL were consisted of cognitive, affective, and behavioral aspects. Both ecological knowledge(KEOC) and environmental skill(SKILL) were determined to serve as two powerful predictors of EL. 3. The level of EL of middle school student was showed statistically significant difference to some variables by student gender, residential area, environmental lesson, environmental concern, environmental information, and environmental activity variables. And the most influential variables of EL in middle school student were environmental skill(SKILL), and locus of control (LOC). Based on the findings of this study, the following suggestions are drawn: It should be established a precise concept on EL as the ultimate aim of environmental education both interdisciplinary cooperation and experts of environmental education and also performed further longitudinal study which assessed multidimensional variables which are able to exactly measure the EL of middle school student.