A clinical decision support system (CDSS) is an interactive application that is used to facilitate the process of decisionmaking in a clinical context. Developing a usable CDSS is a challenging process; mostly because of the complex nature of domain knowledge and the context of use of those systems. This paper describes how a user centered design (UCD) approach can be used in a clinical context for developing a CDSS. In our effort, a design-based research methodology has been used. The outcomes of this work are as follow; a customized UCD approach is suggested that combines UCD and openEHR. Moreover, the GUI developed in the design phase and the result of the GUI evaluation is briefly presented.