Disclosed herein are an in situ-forming, bioadhesive hydrogel and the medical uses thereof. Being formed by in situ crosslinking through an enzymatic reaction, the hydrogel has an advantage over conventional bioadhesive hydrogels in terms of biocompatibility. In addition, the in situ-forming bioadhesive hydrogel has excellent biocompatibility and mechanical strength and has excellent tissue adhesiveness thanks to modification with/without dopa derivatives. The hydrogel finds a variety of applications in the biomedical field, including bioadhesives or hemostats, implant substances for tissue regeneration and augmentation, carriers for delivering biologically active materials or drugs, etc.