Hydrogels have received considerable attention due to their biocompatibility and desirable physical characteristics. Nonetheless, due to their open structure, hydrogels are prone to dehydration in air, resulting in a loss in their elasticity and function. Herein, we report a facile yet effective method for the modification of hydrophobic hydrogel surfaces by using bioinspired amphiphilic Janus silica particles, which are obtained by modifying hydrophilic polydopamine and hydrophobic 1H,1H,2H,2H-perfluorodecanthiol on their two sides via a templating method. With the coating of amphiphilic Janus silica particles, the water contact angles of poly(ethylene imine)-polyacrylamide and polydopamine-polyacrylamide hydrogels significantly increase to 96° and 97°, respectively. Furthermore, we demonstrate that the hydrophobic modification of the hydrogels by Janus silica particles improves the water retention capability, and the overall mechanical properties of bulk hydrogels are not compromised. In addition, we show that hydrogels coated with Janus silica particles not only exhibit hydrophobic surfaces but also have photothermal antibacterial capabilities. Consequently, this study provides a facile method for the fabrication of hydrogels with hydrophobic surfaces, which could potentially be applied to biomedical materials.