Health is the most important asset in life, if health is disturbed (sick) then one's activities will be disturbed. Measles is a highly contagious viral infection, transmission of the infection occurs by inhaling the saliva of a measles sufferer. The measles diagnosis expert system is a system designed as a doctor's aid to diagnose diseases with a dynamic knowledge base. The knowledge system in this system can be classified according to the symptoms experienced so that the user can conclude the disease. Certainty Factor is the method used by the writer to solve problems in this expert system, this system will display questions where the questions are in accordance with the symptoms that have been inputted by the admin (expert) so that the calculation results of these questions are obtained using the certainty formula In the system, login is only used by admins or experts where admin or experts can enter to edit data in the system.