Objective To investigate the conditions for preparing Spirulina platensis protein isolate (spPI) using repeated freeze-thaw cycles, and to compare the physicochemical properties of spPI and commercially processed phycocyanin (cpPC).Methods The effects of soaking time, solid-to-liquid ratio, freezing duration, and number of freeze-thaw cycles on the protein extraction yield were studied. The physicochemical properties of spPI and cpPC were also determined.Results Under the conditions of 16 hours soaking, a solid-to-liquid ratio of 1∶20 (g/mL), 9 hours freezing time, and 10 freeze-thaw cycles, the protein extraction yield reached its optimum at (29.74±0.16)%. spPI and cpPC exhibited their lowest solubility at pH 3 and 4, respectively, and the highest solubility within the pH ranges of 5~7 and 6~7. spPI showed better foaming capacity and foam stability. The strongest emulsifying activity occurred at pH 6~7 for spPI and at pH 7 for cpPC.Conclusion Compared to spPI, cpPC contained higher levels of total thiol, free thiol, and disulfide bonds. spPI demonstrates superior solubility and foaming properties.