Desiccated in room for different times (2--12 hrs), the dehy-dration rates of all four algae reach to ninety percent. Desiccation for 2--12 hrsstimulates the gross photosynthesis rate on Porphyre yezoensis. Desiecated in 7 hrs.the gross photosynthesis rate of Ulva lactusa gets a stimulation, but longcr than 8 hrsit shows inhibition. The same result on Monostroma nitidum: 5 hrs stimulates, longcrthan 6 hrs inhibits. Of all the different desiceation times, Ulva pertusa shows thegroso photosynthesis rate lower than its control. After desiccated for 2--12 hrs, the net photosythesis rate of the four algae all decrease, while in contrast to their respira-tion rates, all increase to some degree.