Findings from assessments of fourth-grade science have indicated that students in Korea scored higher than international averages. Research results have also shown that attitudes toward science were related to achievement outcomes for Korean students. The purpose of this study was to examine the relationship between confidence in science and achievement test scores for a national sample of fourth grade students from Korea who participated in the TIMSS 2011 assessment. Several significant findings were obtained. Students who showed high achievement levels in science were more likely to report that they learned things quickly in science and usually did well in science. Conversely, students who expressed negative comparisons of themselves to others tended to earn lower science test scores. The results from this study indicated that self-beliefs about science were significantly related to achievement test scores for fourth-grade students in Korea.