ABSTRAK The objective of this research is to find out (1) whether there is a significant effect difference between the Integrated contextual teaching learning Approach, the Conventional Approach and Students’ Learning interest on their Mastery of Basic Competence in Science, (2) whether there is a significant effect difference in students with high learning interest and students with low Learning interest on their Mastery of Basic Competence in Science, and (3) whether there is a significant effect interaction between the two learning methods and their Mastery of Basic Competence in Science. This study is an experimental research. The population of the study are all Fourth grade students of state elementary schools in Ngadirojo Subdistrict, Wonogiri. The research sample are 60 students selected with cluster random sampling technique. The study employed a questionnaire to gather data about students’ learning interest. A test was also administered to collect data about their learning achievement in Science. The research data were analyzed using a two-path variance analysis technique. Based on the results of this research, it is concluded that (1) there is a significant effect difference between the Integrated contextual teaching learning Approach, the Conventional Approach and Students’ Learning interest on their Mastery of Basic Competence in Science (F count > F table or 10.355 > 3.11) (2) there is a significant effect difference in students with high learning interest and students with low Learning interest on their Mastery of Basic Competence in Science (F count > F table or 14.612 > 3.96), and (3) there is a significant effect interaction between the two learning methods and their Mastery of Basic Competence in Science (F count > F table or 3.721 > 3.11). Based on the research finding, teachers should be able to arouse students’ interest when angaged in teaching and learning process; Interest plays a major role in achievement the objectives of leaning. Students are expected to be more active in the teaching-learning process evidenced by their willingness to ask question and express their opinion. The teaching and learning process should be supportd by intrastructure and facilities which are needed to improve students’ competence. Keywords : Integrated contextual teaching learning Approach, the Conventional Approach, Students’ Learning interest, and Mastery of Basic Competence in Science