In the present study, we report the first synthesis of diazirine-modified hyaluronic acid (HA-DAZ). In addition, we also produced a precursor polymer solution composed of HA-DAZ and dendritic polyethyleneimine (DPI) that showed strong shear-thinning properties. Furthermore, its viscosity was strongly reduced (i.e., from 5 × 105 mPa s at 10-3 s-1 to 6 × 101 mPa s at 103 s-1), substantially, which enhanced solution injectability using a 21 G needle. After ultraviolet irradiation at 365 nm and 6 mW cm-2, the HA-DAZ/DPI solution achieved rapid gelation, as measured using the stirring method, and its gelation time decreased from 200 s to 9 s as the total concentrations of HA-DAZ and DPI increased. Following UV irradiation, the storage modulus increased from 40 to 200 Pa. In addition, reversible sol-gel transition and self-healing properties were observed even after UV irradiation. This suggests that the HA-DAZ/DPI hydrogel was crosslinked in multiple ways, i.e., via covalent bonding between the diazirine and amine groups and via intermolecular interactions, including hydrogen bonding, electrostatic interactions, and hydrophobic interactions. A lap shear test showed that the HA-DAZ/DPI hydrogel exhibited strong adhesiveness as a fibrin glue following UV irradiation. Finally, the HA-DAZ/DPI hydrogel showed higher tissue reinforcement than fibrin glue in an ex vivo burst pressure test of the porcine esophageal mucosa.