A series of fully bio-based block copolymers (BCPs) consisting of maltooligosaccharides (maltose, maltotriose, maltotetraose, and maltohexaose; A block) and poly(delta-decanolactone) (PDL; B block), with ABA-, A(2)BA(2)-, A(3)BA(3)-, A(BA)(2)-, and A(2)(BA)(2)-type architectures, were synthesized to demonstrate the potential of oligosaccharides as novel hard segments for biobased elastomers. To understand the correlation between the BCP molecular structure and material properties, the BCPs were designed to have comparable molecular weights (ca. 12K) and total numbers of glucose units (12). Morphological analysis revealed the formation of body-centered-cubic sphere and hexagonally close-packed cylinder (HEX) morphologies depending on the branched architecture (interdomain distance 9.7-14.4 nm). While the PDL homopolymer is a viscous liquid due to its low T-g and amorphous nature, all BCPs exhibited elastomeric properties, confirming that the oligosaccharide blocks segregated to form the hard domains to cross-link the rubbery PDL chains. Tensile testing revealed that the mechanical properties of the BCPs were mainly determined by the microphase-separated structure and less affected by the length of each oligosaccharide chain. The HEX-forming A(2)BA(2)- and A(3)BA(3)-type BCPs exhibited Young's moduli of similar to 6 MPa, which is comparable to well-known styrene-based thermoplastic elastomers. Furthermore, a readily available polydisperse maltooligosaccharide was employed to synthesize an A(2)BA(2)-type BCP with a higher molecular weight PDL block (20K), which exhibited a Young's modulus of similar to 6 MPa and an elongation at break of similar to 700%. These results demonstrate that oligosaccharides are a sustainable alternative to the petroleum-derived synthetic hard segments (e.g., polystyrene), thereby opening up a new avenue for fully bio-based soft material design.