The company cannot optimize its computing environment just with individual solutions such as ERP(enterprise resource planning), SCM(supply chain management), CRM(customer relationship management), and KM(knowledge management). EAI(enterprise application integration) has emerged as an alternative that can optimize computing environment of the company through integrating such solutions and systems of distributed computing and mainframe environment. This paper reports the case study of Deakyo Co. in successfully implementing EAI. It describes project goal, project organization, project plan, the implemented EAI configuration and its features, the EAI effectiveness to the firm, and the critical success factors of the EAI project. This case study is thought to be useful as a practical guideline in carrying out EAI project of the company and to provide significant basis for constructing the theoretical framework of EAI project methodology.