An expert system for data analysis S/EXP and its effectiveness. Many kinds of statistical software are available, but most of them require the knowledge and experience of statistics. In such a circumstance a beginner of data analysis usually meets troubles when he starts an analysis without an advisors. We have developed an expert system for data analysis, we call it S/EXP. It is an expert system using S. The system incorporates knowledge and experience of statistics. At present it contains only regression analysis among various possible procedures and the incorporated knowledge and experience are limited, but its effectiveness is recognized. We discuss the possibilities and problems of expert systems for data analysis.