Abstract: This study was designed to determine the protective effects of floridoside on cryopreservation of marine microalgae. Three strains of microalgae were cryopreservated by combination of 10% DMSO and different concentrations of floridoside. After frozen-thaw process, the cell viability was determined by performing flow cytometry with fluorescein diacetate (FDA). Growth curve and physiological parameter (Fv/Fm) were also detected. Results revealed that freezing caused significant decrease on the growth rate of three microalgae, moreover, growth curve and physiological parameters of thawed microalgae were also impacted severely. Combination of floridoside and DMSO significantly improve viability of three microalgae. Especially, 15% of floridoside could increase the cell viability of Porphyridium cruentum by 20% (P0.05) than that only using DMSO. Growth curve were resumed remarkably, and physiological parameter, PSII was also improved. These findings indicated that appropriate concentration of floridoside might be used as a better cryoprotectant to cryopreserve microalgal species, especially P. cruentum. The protect effect was better than sucrose.