Corporate development is carried out to help achieve the corporate's strategic goals and plans. Development begins with analyzing the components that characterize the corporate. The purpose of this study is to determine the condition of the corporate using an open-system diagnostic model which then determines the direction of its development based on the results of the diagnosis. The research subjects were 10 employees with staff and manager levels in one corporate. Data were collected by means of interview, observation and document study instruments. The data were analyzed qualitatively based on the findings of each integrated instrument. Based on the results of the diagnosis, there are several problems that prevent the corporate from improving its work. The most significant problem is the ineffective application of corporate culture that affects all aspects of corporate performance. The form of development proposed is the re-implementation of corporate culture. The diagnostic model provides an understanding in identifying the condition of the corporate from various aspects. The problems identified were intervened in the form of implementing corporate culture in order to improve the quality of its performance.