The defects need to be diagnosed correctly for appropriate remedial measures; otherwise new defect may get introduced. The proper classification and identification of particular defect is basic need to correct and control quality of casting. Keeping rejection to a bare minimum is essential to improve the yield and increase the effective capacity of the foundry unit and also improve the productivity. This work identifies major defects slag and porosity. There are many reasons which generate these defects. So it is preferably necessary to reduce it as much as possible by appropriate analysis of the defects which includes the root cause analysis so that actual reasons behind occurring the defects can be found out to make the corrective action. In this work six sigma technique was used to identify and analyse casting defect. Final result of this work was to reduce the defect by taking corrective action. Tool should be identifying the sources of variation clearly.