The two-step cooling method have been mostly used for the preservation of algae, with cryoprotectants in freezing medium. However, in order to minimize the freezing damages and to get higher survival rate, effect of ice crystal on algae must be reduced in the process of first-step freezing. As size and distribution of ice crystals depend on cooling rate and recrystallization of ice crystal decrease the survival rate, optimal conditions in first-step freezing of cryopreservation must be established. In this study optimal cooling rate and final freezing temperature of Pyropia seriata, Undaria pinnatifida, Sargasum fulvellum were investigated. The mixed suspension of 10% DMSO and 0.5 M sorbitol in 50% seawater used as cryoprotectant. Exothermic temperature, freezing time, latent heat of freezing, temperature range of freezing process were measured by differential scanning calorimetry. Results obtained revealed the optimal cooling rate and final freezing temperature of P. seriata as 1.25oC/min, ?30.5oC, U. pinnatifida, 1.0oC/min, ?27.8oC and S. fulvellum, 1.0oC/min, ?27.1oC respectively.