Science teaching is one of the subjects that has been actively affected by Augmented Reality (AR) technology worldwide. Although the use of AR in science courses is increasing, the effective use of AR still needs improvement. The purpose of this study was to investigate the effect of augmented reality-based argumentation activities in 7th grade students' academic achievement and motivation in teaching astronomy content. The quasi-experimental design was used in this study. The participants consisted of 79 seventh-grade students from three different science classes. The students in experimental group 1 (n=26) participated in an instruction that included both augmented reality and argumentation activities about astronomy. The students in experimental group 2 (n=27) participated in an astronomy instruction that includes only argumentation activities and the students in control group (n=27) received astronomy instruction through traditional methods. The data were collected through pre- and post-academic achievement test and the Motivated Strategies for Learning Questionnaire (MSLQ). ANOVA and Kruskal Wallis tests were used to determine the statistical differences between the pretest and posttest scores of the students. The results showed that augmented reality-based argumentation activities were more effective in increasing students' achievement and motivation than the argumentation and traditional instruction in teaching astronomy.