This study is based on students critical thinking low ability in solving contextual problems which are faced by students. Problems-based learning is one of alternative learning model to improve students critical thinking. The aim of the study is to analyze problems-based learning efect toward improvement of students critical thinking. The method that used is experiment. In this study, experiment class use problems-based learning and control class use conventional learning. Instruments that used critical thinking test. Wilcoxon test result shows that there is difference on improvement of critical thinking ability significantly (α 0,05) between class that use problems-based learning with class that use conventional instruction; there is also difference on improvement of students critical thinking significantly between students with high ability and students with low ability; and there is significant interaction between learning model with students ability toward students critical thinking.