Enzymes are essential biological catalysts, which have merits such as specificity, high efficiency, and mild-acting conditions. Due to the characteristics of enzymes, problems such as poor operational stability and difficulty in reuse limit the practical application of enzymes. These problems can often be solved by immobilization of enzymes. Commonly used enzyme immobilization materials include biochar, chitosan, polymer, and metal-organic frameworks, which often do not match the nature of the enzyme. This study utilizes the self-assembled amino acid hydrogel Fmoc-Y-OMe as the immobilizing material. The hydrogelator Fomc-Y-OMe has advantages like simple synthesis, easy immobilization, environmental friendliness, and good compatibility with proteins. It is able to protect enzyme activity at high temperatures and under a wide range of acid-base conditions and has excellent versatility. In particular, immobilized polyethylene terephthalate degrading enzyme (PETase) can significantly degrade polyethylene terephthalate (PET) film at 70 °C, while free PETase completely loses its catalytic capacity at such high temperatures. The excellent performance of self-assembled hydrogels to protect the catalytic activity of enzymes at high temperatures is highlighted.