This research aims to know about the effectiveness of using PBL in measuring the ability of mathematics problem solving. This research was conducted in 7th grade of Junior High School. The variable in this study was PBL and the ability of mathematics problem solving. Instruments in this research were 5 essay tests of mathematics problem solving ability which were analyzed by testing the hypothesis with t-test. The result showed that average value students who teached by using PBL were higher than students who teached by using conventional model. By using t-test, we know that significant value is less than 0,05, it means that learning by using PBL effective in improving the ability of mathematics problem solving for students.