Abstract: Since the defects causes high rejection rates, it is important to move any production process in the direction of eliminating all imperfections as a part of an effective continuous improvement program. Forging process is no exception to this. In present study, the various forging defects that occur in the components during closed-die hot forging process are investigated initially. The investigation is done with the help of Quality Assurance department in a forging industry. During investigation, the various defects that causes high rejection rates are identified and unfilling defect which has major contribution in high rejection rate is selected for study purpose. The fish-bone diagram is used to explore the possible causes of unfilling defect, through a brainstorming session. It is observed that the three process parameters having major responsibility to fill the job weight. These parameters are- billet weight, heating temperature, and heating time. The best combination of these process parameters must be followed during the production process in order to reduce the rejection rate due to unfilling forging defect. To get the best parameter combination, DOE technique (like Taguchi method) is the most powerful approach. But before going to use Taguchi method, it is very much necessary to determine the effect of selected process parameters on output. Therefore, the objective of this paper is to present the effect/influence of selected process parameters on filling the job weight. For this purpose, OVAT analysis is used here. Engineers and Scientists often perform OVAT experiments, which consists of varying only one factor or variable at a time with keeping others constant.