Wen and Mergen (1999) presented a method for determining the optimum process mean based on balancing the cost of not meeting upper and lower specification limits. However, they have not considered the quality loss for a product which is within specifications in the model. In this paper, we propose the modified Wen and Mergen's (1999) model for determining the optimum process mean consisting of manufacturing cost and quality loss. The quadratic and linear quality loss functions are used in measuring the quality loss of product. The manufacturing cost is assumed to be negatively and linearly proportional to deviation from the target value when the quality characteristic is within specifications and constant manufacturing cost happens when the quality characteristic exceeds specifications.