Diabetes Mellitus (DM) is a chronic disease that occurs when the pancreas cannot produce insulin. Theexpert system seeks to adopt human knowledge to solve problems, usually done by specialists or experts. Construction of expert system in this research using Expert System Development Life Cycle (ESDLC) methodology, Android operating system, Java programming languages, XML and database program using SQLite. The process of disease detection using the certainty factor method. By the certainty factor method, an accurate result obtained from calculations based on the weight of symptoms of the selected user can be provided. From test results, it can be concluded that the results of the application using the black-box method and direct testing by the expert, both the fault functions as well as the disease misdetection processes in the application are not found. This application can perform early disease detection following expert recommendation symptom data. The certainty factor method was successfully implemented in this DM expert system and can provide result a correct percentage of detection with the highest value of 90%. The response on a questionnaire from users determines the validity of disease detection results.

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