This paper suggests a procedure to define business process improvement (BPI) projects with analysis results based on the cause-and-effect chain. The procedure developed in this paper focuses on eliminating root causes of business problems resulted from abnormal events occurred in business process executions. First, we develop three criteria used to make clusters of the root causes where a cluster of root causes will be eliminated together by a BPI project defined based on the cluster. Second, we develop a method to formulate desired expectations from the BPI project. Also, we suggest a method to calculate the relative importance of the BPI projects that help a BPI organization determine priorities of them. We illustrate the procedure and the methods with some examples for the domestic mail delivery process in the postal service industry.