Display omitted •A new bio-inspired design for PDMS sponge has been proposed to improve the absorption capacity for oil-water separation.•The concept of the water absorption and storage functions of cacti plant was applied in designing the PDMS sponge.•The sponge with microscale architecture was fabricated by 3D printing technology.•The new design showed an absorption capacity increased by about 3.7 times in the test of oil-water separation. Oil spills from disasters such as the sinking of ships and the discharge of oily wastes cause serious environmental problems. Polydimethylsiloxane(PDMS) sponges are valuable tools for isolating spilled oil. Here, we propose new PDMS sponges with bio-inspired design and enhanced absorption capacities. 3D printing was used to produce templates having negative designs, and after being filled with PDMS, the templates were selectively dissolved. Through this, PDMS sponges with well-interconnected and controlled porosities were produced within 10% error. The wettability of sponges with various pore sizes and line widths was investigated. The surfaces were found to be highly hydrophobic, with water contact angles of 100-143°, and oleophilic, with oil contact angles of ∼0°. The sponge fabricated with line width of 200 μm and pore size of 400 μm showed the highest hydrophobicity and oleophilicity. These parameters were used to produce the surfaces of hollow sponges having bio-inspired design that mimics the water absorption and storage functions of cactus. Repeated oil-water separation testing was conducted, and the absorption capacities were compared with those of non-hollow and conventional sponges. The new design showed absorption capacity up to 3.7 times that of the sponges. The bio-inspired PDMS sponge provides a significant advance in oil–water separation ability.