Developing adhesive materials that can selectively degrade into non-toxic by-products is a key challenge in materials science, particularly for short-term implantable devices and tissue regeneration treatments. Herein, we leverage biodegradable phytoglycogen (PG) nanoparticles (highly branched glucose polysaccharide nanoparticles) as scaffolds for coupling adhesive dopamine motifs to be used as biodegradable underwater adhesives. Phytoglycogen-dopamine (PG-dopa) hybrid nanoparticles could be synthesised in an aqueous solvent, to which the products retained a similar size and particle morphology to the initial PG nanoparticles. The PG-dopa nanoparticles could readily be assembled into dense monolayers on silica substrates through a simple dip-coating procedure. Colloidal probe atomic force microscopy was used to characterise underwater adhesiveness, where it was found that the films produced strain energy release rates approaching 8 mJ m⁻² between hard silica materials. Importantly, the PG-dopa films retained the original biodegradability towards glucosidase enzymes, which can degrade the adhesives in fluids containing these enzymes over time (e.g., 45 U mL⁻¹ of α-amylase solution degraded the majority of the adhesive films in 30 min). Given the inherent biocompatibility of glycogen materials, we anticipate these adhesives having application in short-term implantable devices.