Cattle and other animal products contribute 15 % of GDP and 33% of the agricultural output of the country. Although, cattle have a significant role in the development of economy, cattle diseases resulted in low productivity and a significant obstacle to international market access. Detecting cattle diseases and treating them will improve the productivity. In Ethiopia, the ratio of veterinarians to animals is 1:500,000. To reduce this ratio, animal health assistants have been deployed to treat cattle in the country. But animal health assistants have only basic knowledge about cattle diseases. Their knowledge has to be upgraded from time to time with regard to cattle diseases. This may not be possible through veterinarians as their number is few. To address this problem, a web based expert system for diagnosing infectious and non-infectious cattle diseases has been developed. The proposed system is composed of knowledge base, inference engine and user interface which are the main components in expert system. The system integrates a structured knowledge base that contains knowledge about symptoms of cattle diseases. In addition to diagnosing diseases, the system allows the users to view diseases detail, post and view current dangerous cattle diseases. The system has been evaluated by domain experts (veterinarians) and animal health assistants and the analysis of the result shows that the system is acceptable. Keywords: Amharic knowledge base, Infectious Cattle Diseases, Non-Infectious Cattle Diseases, Cattle Diseases Diagnose System, Web-based Expert System