The purpose of this research is to know Just In Time partnership analysis at UD. Bintang Mandiri Purworejo. Sampling using internal purposive sampling technique. Internal purposive sampling is a decision taken by the researcher about who to interview, when to make observations, what documents or how much documents to review. This research uses Content analysis method Based on the research that the authors do ultimately obtained the results of research that is the behavior factor into a unity that can not be separated to get positive benefits. This means that behavioral factors such as trust, interdependence and alignment of objectives when their activities are applied in a relationship, will form a good and ethical relationship. From this relationship will support the success of an attempt to implement the system of Just In Time (JIT). Given the behavioral factors, good relationships are established and the realization of a Just In Time (JIT) system in which behavioral factors have a positive impact on the successful implementation of Just In Time (JIT) systems. Keyword: Partnership Just In Time, Behavioral Factors, Good relationship and ethical