We built and implemented an expert system capable of diagnosing poultry diseases by simulating computer programs using "Prolog" language. Depending on expertise taken form experts, book scientific magazines and applied studies on diseases of poultry animal medical centers in the situated in governorate. A number of interviews and live observations have been conducted where knowledge was edited, ordered and put into special structure in the language used in writing and programming the system A number of very common diseases have been selected equals (l3) diseases to be diagnosed by a series of symptoms of each disease. Knowledge has been incorporated into the expert system by using inference rules. The system depends on an interactive style to interface with the use by using menu driven method. The ultimate linal results have been presented to the expert system alter lasting stage which includes three medical centers in the governorate where the system has been applied to (120) case studies and the expert system has proven its efficiency in the test.