Purpose: In this study, it is aimed to improve the production process by applying the 5S method in machining applications in a company operating in the field of aviation and defense. Theory and Methods: The pilot area, where the 5S application will be made the toolroom, which is one of the most important points of machining, has been selected. The necessary methods to implement the 5S steps in the toolroom were analyzed and the necessary forms were prepared. With the trainings, the logic of the lean thinking system was explained to the company personnel. With these trainings, firstly, the steps to be implemented within the scope of 5S in the production process, secondly, how they will be implemented, thirdly, the purpose of the changes to be made during the implementation phase and last, the planned targets to be achieved are clearly explained to the employees. Within the plan, the steps of sorting, organizing, cleaning, standardizing and discipline were successfully implemented. 5S planning was worked on in June 2020 for the toolroom, and after this month, production was carried out according to the 5S order. Outputs, such as defective part rates, machinetool idle rates, toolroom expense and tool preperation time were determined as performance evaluation criteria. Results: As a result of the 5S application, a high rate of improvement was achieved in the toolroom section of the company. According to the results obtained, 66% improvements were observed in the cost of the toolroom, 76% in the downtime of the machines due to the toolroom, 78% in the scrap rate due to the faulty cutting tool, and 85% in the unnecessary movement load rates in the toolroom. In the gray relational analysis of the outputs, the most productive month in terms of production was determined as November, and the most unproductive month was April. Conclusion: 5S application has been demonstrated that the company of CRN Aerospace Hypertechnology Defence Inc. can be successfully applied to the toolroom. According to the performance criteria, the results observed for the first 5 months of 2020 and the 5 months after June revealed the importance of the 5S study.