As an extension of fiber-reinforced plastics, research on fiber-reinforced soft hydrogels has attracted remarkable attention. From the perspective of sustainability, it is desirable to use biopolymers such as cellulose and chitin as the fibrous phase of these hydrogel composites. However, obtaining biopolymer-based fibers from plants or fungi generally requires environmentally harmful processes such as extraction, purification, and reconstruction of the target biopolymers. To avoid this problem, this study aimed to obtain tough biopolymer/hydrogel
composites with minimal environmental impact. Specifically, minimally processed eringi (king oyster
mushroom) and kanpyo (dried shaved gourd) were directly used as the fibrous phase, and hydrogel matrices were prepared within them to make the bio-composites. The hierarchical fibrous structure of the biopolymers inherently present in eringi and kanpyo was well preserved in the bio-composites. The resulting composites exhibited high strength and toughness originating from the well-aligned fibrous biopolymers in the bio-composites.