The objective of this study is to describe students' preconception of some electromagnet topics. The data obtained using the Three Tier Electromagnet Test which consisted of 18 items. This test was given to 328 twelve-grade students of the public senior high school in Bali. According to the students' response to the test, students' preconception could be categorized as a scientific concept, misconceptions, lack of concept and error. The data were analyzed descriptively. The results showed that

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... verage of 14,58% of students has a scientific concept, 27.86% of students experience a misconception, 39,99% of students experience lack of concept and 17,53% of students experience an error. It can be concluded that students' prior knowledge were very diverse. It is important to indentify students' preconception on electromagnetic as a consideration for effective conceptual change strategy.