Today, the raising of competitive power in parallel with developments in technological and production system fields has caused firm product prices to gain more importance as regards entering and attaining permanency in the market. So, it is very important that product costs are determined by the enterprises in a suitable and reliable way. In this thesis, an Activity Based Costing (ABC) system is presented related to product costing, and by using this system a problem was solved in a watergoods firm. An application guide is prepared in order to follow a proper implementation roadmap. Initially, the existing cost building system of the firm is investigated and the problem is defined in the company. The ABC system is used to solve the problem. A comparison of the results of ABC and the traditional costing system was also presented at the end of the project and the results are evaluated.