The aims of this study are to elaborate the instructional strategy to develop metacognition of junior high school students in observation / experimental activities and to examine the effect of the instructional methods. The instructional methods was elaborated based on the result of the junior high school students' metacognition in observation / experimental activities.The elaborated instructional strategy adopted five methods, as follows: (1) instruction of the self-control strategies, (2) bulletining the learning plan, (3) improvement of questioning techniques, (4) utilization of flash cards, (5) devising worksheets. The lessons were performed for 70 junior high school students (years 1) to examine the effect. The result of this study supported the effectiveness of the elaborated instructional strategy for developing students' metacognition in observation / experimental activities.