To assure efficient expatriate assignments, the objective of this study is to establish prediction rules of employees' expatriation willingness using the rough set theory and decision tree. We summarize 22 impact factors from literature regarding expatriation willingness and utilize them to develop a questionnaire. A total of over 400 questionnaires are returned and effective for data analysis, resulting that one factor is removed. The adoption of the rough set theory classifies these factors into three categories. Among them 18 out of 21 factors are set as the inputs for the decision-making model to construct the prediction rules of employees' expatriation willingness. Six rules regarding the refusal of expatriation assignments and three rules regarding the acceptance of expatriation assignments are found. The rules can be valuable to employers in making decisions of international expatriation.