Intrinsic self-healing hydrogel materials have been studied by many researchers owing to their excellent durability and high applicability in the biomedical field. Herein, we report a self-healing hydrogel containing dynamic boronate ester bonds. First, low-molecular-weight hyperbranched polyglycerol (LMPG), containing cis-1,2- or 1,3-diols, was synthesized by cationic ring-opening polymerization of glycidol initiated from citric acid. Second, 4-vinylphenyl boronic acid and acrylamide were co-polymerized in the LMPG-containing alkaline solution used for preparing the hydrogel. The composition of vinyl monomers, LMPG, and chemical cross-linker affects the gel-formation and self-healing properties of the hydrogel. Interestingly, the prepared hydrogel with specific composition exhibits excellent extensibility, resulting in 416-fold (41,600%) elongation. The formation of a reversible boronate ester bond by a diol of LMPG and boronic acid of vinyl polymer enables flexible fiber spinning process by reducing the drawing stress. After fiber fabrication is completed, the reversible bonds act as permanent multi-cross-point under absence of water, thereby giving a high tensile strength (128 MPa) to the hydrogel-based fiber.