In the era of software metrics demand for quality software has undergone with rapid growth during the last few years. This is leading to an increase in the development of metrics for measuring the properties of software such as coupling, cohesion and inheritance that can be used in early Quality assessments. Much effort has been developed to the development and empirical validation of software metrics. Quality models that explore the relationship between these properties and quality attributes such as fault proneness, maintainability, effort or productivity are needed to use these metrics effectively. The goal of this work is to empirically explore the relationship between Object Oriented Design Metrics and Fault Proneness of object oriented system classes. We empirically analyzed and tested by Open Source Java projects.