Expert system is a system that uses human knowledge to solve a problem that generally requires an expert knowledge. In this case, the expert system is used in a poultry farm that has a variety of diseases, especially from infectious diseases such as Tetelo and avian influence could quickly infect cattle and can cause a great loss if handled later. The purpose of this study was to design and build an expert system application for diagnosing and treatment of diseases in poultry. This expert system was made by forward chaining inference method and designed by Dreamweaver CS4 along with JSP as its programming language. The process of working on this expert system is the user to diagnose based on caused symptoms and the user will get the disease and its prevention. With the existence of this expert system, the user especially poultry is expected to conserve capital production which in this case for charge a veterinarian to diagnose and manage disease in cattle chicken.