A data base which consists of 415 records of fire and explosion accidents in chemical plants were prepared・ These data were arranged by items such as working situation,apParatus and equipment,kind of combustibles,type of ignition source,direct and indirect causes etc,Correlation coefHcient between each two items was also calculated,An expert system w}1ich contains the data base and the coefficients was deveioped to pred1ct the¢ause of accident. By answering to the questions conceming each item which is shown on the computer display one by one,the lirect cause is given as estimation result, The expert system is expected to give the correct answer rate of 90% for known accidents and 70% for unknown ones.