Abstract: An optical and transmission electron microscope study on nerve tissue of thoracic ganglion and muscles in the crab,Eriocheir sinensis which suffering from tremor disease,indicated that rickettsia-like organisms (RLO) infested in glial cells,connective tissue and intercellular space.In the connection between nerve and muscle fibers-motor end-plate,there were also a lot of RLOs in groups,just like the way in the nerve tissue.Thoracic ganglion is a nerve plexus controlling the moving of periopods.The fact that RLO infested this tissue and the motor end-plate verifies that RLO closely relates to the tremor disease,which main disorder is paroxysmal tremor of the periopods.This is firmly confirmed that RLO is a pathogenic parasite of the tremor disease.