An expert system is a computer program designed to imitate the decision-making abilities of an expert in a particular field, combining knowledge and rules obtained from experts to diagnose problems, provide advice, or make complex decisions, especially in computer LAN network disruptions, so this is needed application of an expert system for troubleshooting computer LAN networks for users which supports the diagnosis process using the certainty factor method, with an explanation of the certainty factor which has a concept based on symptoms and diagnosis from the weight of an expert's value and the user's value, then calculated using the formula in CF, the final result is the creation website-based computer LAN network troubleshooting expert system.