Abstract: An expert system for gas chromatography used in pharmaceutical analysis is intro-duced.The expert system, which consists of six main modules ,that is knowledge base ,inferenceengine ,user interface ,module for knowledge acquisition , dynamic database and medule forchromatographic optimization, is implemented by using AI language Turbo Prolog and is operated onIBM PC/XT, Preduction rule is used to represent the knowledge and forward chaining is applied togive deduction。 Nearly 2 ,000 of chromatographic data of different kinds of drugs and related com-pounds are kept in this system。It has several functions such as judgemet for separation mede,recommendation for column system,knowledge acquisition and chromatographic condition optimiza- tion.