Understanding of the ice crystallization process and cell mebrane kinetics during cryopreservation plays a key role in storaging cells. Here we synthesized poly(ethylene glycol)-poly(L-alanine) block copolymers with various block length. Depending on the block length, size of ice crystals varied, and the shape was also diverse from spherical to rod-like sharp shape depending on the concentration and the kind of polymers. Stem cell recovery improved as the size of ice crystal decreased, however it dropped as the ice crystal shape was rod-like shape. Cell recovery also seems to be affected by cell membrane stabilization through the polymer. The recovered cell exhibited excellent proliferation and underwent into osteo-, chondro-, and adipogenic differentiation. Contrary to dimethysulfoxide (DMSO), current cryoprotectant, PEG-PA proved to be cytocompatible. The paper suggests that P1 among PEG-L-PAs can be an excellent cryoprotectant for stem cells to replace cytotoxic DMSO.