This study aimed to describe students' ability of mathematical reasoning in SMP Alam Al-Aqwiya Cilongok. This study applied descriptive qualitative method and the subject of this research was the eighth graders of class C SMP Alam Al-Aqwiya Cilongok in academic year of 2017/2018. The technique of selecting research subject was purposive sampling. The students were grouped into three; high, medium, and low motivated students. Each group was represented by two students. The method of data collection used test, interview, and documentation. The techniques of data analysis were data reduction, data presentation, and conclusion. The results of mathematical reasoning ability in high motivated group showed that the students were able to propose assumption, to manipulate mathematics, and to make conclusion from statements. Different from the previous group, medium motivation students were able to propose an assumption, but they still centered to variables commonly used, able to manipulate mathematics, able to make inappropriate conclusion. Furthermore, in low motivated group, the students were unable to propose an assumption, unable to manipulate mathematics in choosing the procedures to solve mathematics problems on Linear Equation System of Two Variables, and unable to make conclusion.