Background: Flu and the common cold are both respiratory illnesses but they are caused by different viruses. Because these two types of illnesses have similar symptoms, it can be difficult to tell the difference between them based on symptoms alone. In general, flu is worse than the common cold, and symptoms are more intense. Colds are usually milder than flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations. Flu can have very serious associated complications. Objectives: The main goal of this expert system is to get the appropriate diagnosis of disease and the correct treatment. Methods: In this paper the design of the proposed Expert System which was produced to help Medical Practitioner in diagnosing Cold and Flu diseases. The proposed expert system presents an overview about Cold and Flu diseases are given, the cause of diseases are outlined and the treatment of disease whenever possible is given out. CLIPS and Delphi languages were used for designing and implementing the proposed expert system. Results: The proposed Cold and Flu diseases diagnosis expert system was evaluated by in-house Trials. Conclusions: The Proposed expert system is very useful for Medical Practitioner, patients with cold and flu diseases and newly graduated practitioners.