Abstract: To explore whether abscisic acid (ABA) and cold adaptation can improve the cryopreservation efficiency of Porphyra sensu lato, the free living conchocelis of Pyropia haitanensis were treated with ABA (100 μmol/L) for 48h at 20℃, light intensity of 40 μmol·photons/(m²·s) with photoperiod 12L﹕12D or cultured in dark at 4℃ for 6 days before cryopreservation at –80℃. The effects of cryopreservation were evaluated by continuous measurement of algal survival rate after frozen, the maximum light quantum efficiency (F_v/F_m) of PSⅡ and the expression of cold adaptative related genes, such as P(H⁺)-ATPase, ald, Mn-sod A, Cu/Zn-sod 1, apx-2, hsp70-4, psy-2, gapdh, and gpxha-1. The results showed that: (1) Both ABA treatment and cold adaptation at 4℃ increased the survival rate of P. haitanensis conchocelis after cryopreservation, 59% in the ABA groups and 89% in the cold adapt groups; (2) The F_v/F_m of the conchocelis after cold adaptation recovered significantly faster than those of the other groups (P<0.05), with the optimal level after 35 day culture; (3) ABA treatment and 4℃ cold adaptation significantly up-regulated genes like P(H⁺)-ATPase, ald, Mn-sod A, Cu/Zn-sod 1, gapdh (P<0.01) and psy-2 (P<0.05) in the algae, but only ABA induced apx-2 and hsp70-4 (P<0.01). In summary, ABA treatment and cold adaptation can improve the frost resistance of P. haitanensis and improve the efficiency of cryopreservation. The cold adaptation method at 4℃ is simple and effective, and has greater application potential.