Diabetes mellitus is a chronic metabolic disorder, requiring vigilant monitoring of blood glucose levels. In this study, an injectable fluorescent enzymatic hydrogel was designed for rapid glucose detection. The leakage-free glucose-responsive hydrogel was constructed by the covalent linkage of a multi-arm poly-(ethylene glycol) (PEG), bovine serum albumin (BSA), glucose oxidase (GOx), and 4-(aminomethyl)-6,7-dimethoxycoumarin (Coumarin-NH2). The GOx serves as glucose-recognition element and the pH-sensitive Coumarin-NH2 as a fluorescence turn-on reporter. The material properties of the fluorescent hydrogel were systematically characterized which show high elasticity with good mechanical strength. Upon the addition of glucose, the as-developed fluorescent hydrogel shows a fast response time, good sensitivity, and good reproducibility at physiological pH and ambient temperature. The glucose-sensing mechanism is based on the oxidation of the glucose by GOx that generates protons to change the local pH. Consequently, protonation of the covalently immobilized and pH-sensitive Coumarin-NH2 turns on the fluorescence of the coumarin. The fluorescence hydrogel developed holds great promise as an injectable, implantable glucose-sensing biomaterials for in vivo continuous glucose monitoring.