Spasticity is a motor disorder encountered after upper motor neuron lesions. It adversely affects quality of life in most patients and causes long-term burden of care and has significant financial implications. The effect of conventional therapies for spasticity including physical therapy, surgery, and pharmacotherapy are not always satisfying because of the short-term effects or side effects in some patients. Acupuncture is a part of traditional medicine originating from China. It has been used to resolve functional recovery problems after central nervous system injury for many years in Asian countries and is increasingly popular in western countries. Some researches suggest that acupuncture has therapeutic potential to help improve limb movement function and decrease the severity of spasticity. This review synthesizes studies involving stroke, brain injury, spinal cord injury, cerebral palsy, and multiple sclerosis to give an overall picture of the effect and potential mechanisms of acupuncture on spasticity occurring after upper motor neuron lesions. Moderate-quality evidence suggests that electroacupuncture combined with conventional routine care (pharmacological/rehabilitation) could reduce spasticity and improve motor function and activities in daily living after stroke. However, there is not enough evidence to conclude that acupuncture (including electroacupuncture) could reduce spasticity with other central nervous system diseases.