The goal of this study is to propose the effective method of investigating the injurious factors and making improvement plans that prevents the workers against musculoskeletal disorders at metal product companies and the same business field with similar working conditions and process. A questionnaire were adopted to analyze the symptoms of workers` musculoskeletal disorders, and an ergonomic assessment method such as RULA, OWAS were performed to find out harmful factors of workplace and working posture. Based on the result of the evaluation, to enhance the working environment, improvement of worktable, working space, tools, and outfit was suggested, and induction of mechanical system was also suggested. It can be concluded that the method and process described in this paper could be helpful for diagnosing the musculoskeletal disorders and making improvement plans to the metal product companies and the same business field with similar working conditions and process.