Motor nerve diseases are a group of neurological disorders that cause gradual loss of muscle strength. Motor nerves are divided into two types, namely upper motor neurons and lower motor neurons. The UMN originates in the brain and is responsible for sending signals from the brain to the brainstem or to the spinal cord. While the LMN originates from the brain stem and spinal cord, and functions to transmit signals to all muscles. The signals sent are used to regulate body muscle movements, such as walking, gripping, breathing, speaking, or swallowing. When motor nerve function is disturbed, the sufferer will find it difficult to carry out these movements. Problems that occur in the RSU. Mitra Medika Medan in the process of consulting patients who experience motor nerve disease problems, namely the process of diagnosing motor nerve diseases using the services of an expert doctor in the field of motor nerve disease diagnosis by consulting conventional methods, the time needed to serve many patients is less efficient, so long queues can be avoided. so that not a few patients feel disappointed. Overcome problems that occur in RSU. Mitra Medika Medan, it is necessary to have a tool in the form of an expert system that provides diagnostic results in accordance with expert knowledge. Therefore, in this study, the authors built an expert system for diagnosing motor neuron disease using visual-based visual basic net 2008 by applying the Mamdani method as a method of solving diagnostic problems in the expert system that was built