One of the causes of death in humans is lung disease, namely cancer. Data from the Indonesian Cancer Information & Support Center (CISC) shows lung cancer is the number one cancer killer with a total of 14 percent of cancer deaths. The death rate due to lung cancer in Indonesia even reaches 88%. That must be considered to be one of human efforts in maintaining health in the lungs. Handling that can be done is to check early to be able to avoid or treat the lung disease. The existence of an expert system provides a solution to overcome this. Expert system is a computer system that stores knowledge, facts, reasoning and experience from an expert that is used to solve problems in a particular field, especially for lung disease. The purpose of this research is to design an expert system of web-based lung disease diagnosis that can help the public to carry out consultations about lung disease anywhere without having to come directly to the hospital or puskesmas/clinic. The method used is descriptive method and action. In designing the expert system, the method used is the method of object-oriented approach and prototype development method. With this expert system, it will be easier for the public to obtain information about lung disease, help the public and doctors to diagnose lung disease, and help doctors supervise the treatment of patients and the public.