Through sampling thalli from suffered sea area,the discoloration of Porphyra yezoensis was studied by photomicrography and electron microscope technique.And preliminary quality test was conducted on dried laver,Porphyra yezoensis that suffered from discoloration as well.The results of microscope-observation showed that,diseased thalli cells had large vacuoles,their chloroplasts atrophied or crushed to the edge of cell,several cells at the base died,and floridean starch particles manifolded under electron microscope.Quality test showed that total suger contents of faded dried lavers were apparently higher than those in normal dried lavers,while crude protein,fat,photosynthetic pigments and free amino acids in diseased laver were lower than normal dried lavers.Especially,the percentage of three flavour amino acids(Asp,Glu and Ala) in faded lavers was extra low.These influenced the quality of lavers greatly and resulted in inferior quality.The results of the absorption spectrum on the normal thalli and diseased thalli demonstrated again that the content of photosynthetic pigments in thalli that suffered from discoloration is extremely low.When we added nitrogen in seawater to culture the diseased thalli,the color restored more or less and thallus cells returned to normal after 6 days.