In this paper, our aim is to examine the effect of project based learning on 7th grade students' mathematical success in "Ratio, Proportion and Percentage" unit and attitudes towards mathematics. This study was implemented with 70 7th grade students of Atatürk Primary School in Eminönü District in Istanbul. Before starting the implementation, experiment and control groups were subjected to pre-test and mathematic behaviours scale. In the experiment group Project Based Learning was conducted whereas the control group was taught with traditional method. At the end of the study, both groups were subjected to final test and mathematic behaviours scale. Besides, the experiment group was given "Activity Evaluation Form", "Self Evaluation Form" and "Students Observation Form". Data obtained from the research were analyzed and interpreted with statistics programme. Video records of the students' project presentations are also available. The paper will also show the interesting as well as the important results of this research in all aspects.