Lightweight composite coil springs are still limited in their practical applications by costs of raw materials, resin impregnation and eco-environmental factors. Here, we fabricated a natural bamboo coil springs (BCS) via a facile hydrothermal-molding-fixing (HMF) treatment using moso (Phyllostachys edulis) bamboo slivers (BS). The BCS was superior to plant fiber-reinforced composite springs in terms of mechanical properties, dimensional designability and costs. The BCS basically inherited the cell structure and mechanical properties from natural BS, showing massive shrinkages of parenchymal cells and the occasional inter-fiber cells cracks, as well as the partial removal of lignin and hemicellulose after HMF treatment. Moreover, the BCS showed a stiffness retention rate of 86.3% after undergoing 8000 large-deformation compression cycles, demonstrating its high structural stability. The structure-function-compositions relationships of bamboo cells will help the design and manufacturing of curved bamboo furniture and structural bamboo coil springs for cushions application.