The ability to think mathematically includes many mental activities which involve the workings of the brain. To describe students' mathematical thinking ability, one of the efforts that can be done is to apply the mathematical problem-based learning model. It involves students to solve a problem through scientific method stages, so that students can learn the knowledge related to the problem and also have the ability to solve the problem. This study aims to describe students' mathematical thinking ability through Mathematical Problem-Based Learning Model.This type of research is qualitative. The subjects of the study were senior high school students in the city of Parepare. The data collections were conducted by observing the learning process in class and giving the assignment/test to the students. The collected data were then analyzed qualitatively. Based on the results of research and discussion it is concluded that the students ability to think have sequences in the activities of mathematical thinking with the application of mathematical problems-based learning model. Therefore, the students' mathematical thinking ability is described as follows: (1) identification stage of the problem, (2) the grouping stages, and (3) drawing conclusions.