This thesis examines the association between capacity utilization and profit margin. Using the hand-collected data about capacity utilization disclosed by listed firms in Taiwan for the investigation, this study obtains the following findings. When there exists un-utilized capacity, the rate of capacity utilization is positively associated with profit margin. But when the capacity is fully utilized, there is a negative association between capacity utilization rate and profit margin. Further, when companies expand their capacity by capital expenditure, the higher the utilization rate, the higher the profit margin.