The purpose of this study was to explore the effects of students’ self-efficacy and STEM Lego robots teaching (Science, Technology, Engineering, and Mathematics) on students’ academic achievement and learning attitude. A quasi-experimental research method was used in this study. The participants were 52 sixth-grade elementary school students in Hsinchu. Moreover, a 3-week Lego robot curriculum was designed. The result of two-factor multivariate analysis of variance showed that no interaction between self-efficacy and STEM Lego robots teaching on academic achievement and learning attitude was found. Besides, the result showed that STEM Lego robots teaching did not have significant influence on academic achievement and learning attitude. Although students’ self-efficacy did not have significant influence on academic achievement, it was found that students’ self-efficacy have significant influence on students’ learning attitude. The students with higher self-efficacy had better learning attitude than students with lower self-efficacy.