The aim of this research is to determine whether the use of augmented reality applications in the teaching of the subject of ''Geometric objects'' in the sixth grade mathematics class has an effect on the development of students' geometric thinking levels and spatial ability. The research was conducted using a pre experimental design, one of the quantitative research methods. The research was carried out with 15 sixth grade students studying in a state secondary school in Aziziye district of Erzurum province in the spring semester of the 2021/2022 academic year, for 15 class hours which each of the lessons consist of 40 minutes. While collecting data in the research, van Hiele Geometric Thinking Test, Middle Grades Mathematics Projects (MGMP) Spatial Ability Test and the Geometric Objects Achievement Test were used. Statistical package program was used in the analysis of the data. As a result of the analysis of the data obtained from the van Hiele Geometric Thinking Test, the MGMP Spatial Ability Test and the Geometric Objects Achievement Test, it was determined that there was a statistically significant difference between the pretest and the posttest in favor of the posttest. It concluded that teaching geometry with augmented reality applications had a positive effect on the development of students' geometric thinking levels and spatial ability, and in addition, it had a statistically positive contribution to their academic achievement. Therefore, in line with these results, it can be said that augmented reality-based teaching applications offer new opportunities for learning- teaching processes.