This paper describes a knowledge based system employing certain expert system rules to detect kind of measles disease. A rule based expert system is designed for early diagnosis of measles disease. Simplified rules were used to determine the base of rules. In order to simplify the rules, Boolean simplifying method was used. Front diagnosis plays an effective role in determining and therapy. Front diagnosis gives an easy position to the doctors during the therapy and diagnosis. With an expert system that will be applied as an example before the patient does not come to the doctor, a test will be applied and front information will be taken from the patient. In this study, a logic system was developed to diagnose the measles and diseases showing symptoms similar to the measles.