This research is a quasi-experimental study aimed to determine the effectiveness of the implementation of model Problem Based Learning (PBL) in terms of student’s mathematical prolem solving. The research design was posttets control design.  The population in this study were all seven grade students of SMPN 1 Jati Agung in the academic year 2012/2013 and the sample of this research are student of class VII-A and VII-D randomly selected from four class there. Based on the data analysis, found that the average of student’s mathematical problem solving in PBL is higher than conventional learning and student learning completeness more than 50%.   The conclusion that can be draw from this research is that model PBL is effective in terms of student’s mathematical problem solving ability.Key words: Effectiveness, PBL, Mathematical Problem Solving