The purpose of this study was to describe the ability of students’ mathematical modeling when completing PISA problems of formulation category. As many as 310 seventh grade students were involved to solve PISA quantity problem. The students’ mathematical modeling responses were assessed by using the stages of understanding the problem, creating mathematical models, solving mathematical models, interpreting mathematical results in real situations, and validating solutions. Results indicate that there are three types of mathematical modeling found from the students’ responses. Type 1, students wrote important information and what is asked on the problem, brought up variables to think about what is asked to the problem at the stage of understanding the problem. In this type, students created mathematical models in the form of linear inequalities of one variable, and solved them using the rules of inequality. Finally, they drew on conclusions to interpret mathematical results in real situations and validating the solution by substituting the results. Type 2, the students wrote important information on the problem and what is asked on the problem. Students wrote an implicit mathematical model in the form of a difference in the linear equations of two variables and completed the mathematical model by involving the subtraction. Finally, they made conclusions to interpret mathematical results in real situations, although the did not validate the results obtained. Type 3, the students wrote important information on the problem as well as mathematical models in the form of two variables linear equations and the results are outlined in tabular form. The completion of the mathematical model was indicated by comparing the values ​​obtained in the table. Finally, students also made conclusions to interpret mathematical results in real situations, although did not validate the results obtained.