The present work was concerned with the olpidiops-disease of Porphyra yezoensis which occurred in southern part of Jiangsu province from 2004 to 2005. The research of the symptom and course of this disease was performed to affirm that the pathogen is Olpidiopsis sp.. The experiment of the effect of a series of different factors such as temperature and density on this disease was also conducted, the results shows that high temperature, high salinity and high density all accelerate the infection of the pathogen, and that properly increase the dried time of the thallus could slower the spread of pathogen in a certain extent. So far, frozen-storage net is the primary method in the prevention and cure of this disease. Otherwise, after researching and verifying the data about the classify of fungi, it was found that the Chytridiales and Olpidiopsis belong to different orders, so the name of this disease should be corrected from Chytrid-disease to olpidiops-disease.