The purpose of this study is to examine how cost classification is used in management accounting and to what extent this information is used in the management decision-making process in manufacturing companies. Cost categories, such as fixed, variable, direct, and indirect, help managers understand the cost structure and assess operational efficiency. This study was conducted through a qualitative descriptive case study approach in one of the manufacturing companies in Indonesia. Direct observation, in-depth interviews, and internal company documentation were used to collect data. The results showed that, especially in budget planning, cost-volume-profit analysis, and selling price determination, proper cost classification plays a significant role in the decisionmaking process. However, some problems were found with the consistency of cost classification, which can affect the accuracy of management data.