The hydrogelation of amphiphilic triblock copolymers based on the poly(ethylene glycol) (PEG) and the sheet-like polypeptides was studied in this report. The triblock copolymers were synthesized by ring-opening polymerization (ROP) method using PEG-diamine with two different molecular weights as the hydrophilic initiators and polypeptides of two _L-cysteine derivatives (S-methyl-_L-cysteine and S-benzyl-_L-cysteine) as the sheet-like, hydrophobic segments. The experimental data revealed that the polymer chain length, block ratio, and functional group on the side chain would dictate the amphiphilic balance and non-covalent interactions between the polymer chains, which consequently influence the hydrogelation of triblock copolymers and their hydrogel mechanical properties. The sheet-like poly(S-benzyl-_L-cysteine) (PBLC) was found to be a good hydrogelator whilst the samples containing poly(S-methyl-_L-cysteine) (PMLC) could not form hydrogels with polymer concentrations below 10 wt%. This study highlighted these amphiphilic triblock copolymers synthesizing by tethering sheet-like, hydrophobic polypeptide segments on both ends of a hydrophilic polymer could be an effective strategy for preparing hydrogels with tunable properties.