Room-temperature sodium-based batteries have the potential for meeting large-scale grid energy storage needs. Inspired by the advancement of the design and building of electrode materials in lithium-ion batteries, improved nano-architectured electrodes can be created for sodium-ion batteries, allowing increased electron transport kinetics and conductivities. Here, nanocomposites with 3D porous structures are reported as a high-capacity anode material for sodium-ion batteries by using an easy, low-cost and environmentally friendly synthesis of pyrolyzed bacterial celluloses (PBCs). Bacterial celluloses (BCs) produced by the Gluconacetobacterxylinus strain are pyrolyzed at 500, 750 and 1000 C, resulting 50, 130 and 110 mAh g-1 capacities over 80numbers of cycles, respectively, in the presence of the binary ethylene carbonate–propylene carbonate mixture. In order to increase the cell performances, in situated SnO₂ nanoparticles with bacterial cellulose(SnO₂@PBC) are produced by addition as synthesized5-nm-sized SnO2 nanoparticles into the BC growth medium together with the G. xylinus strain. Following the pyrolysis at 500 C, the SnO₂@PBC composite is better able to handle the accommodation of the dramatic volume change of the incorporated SnO2nanoparticles because of the interaction of oxygen-containing moieties of bacterial cellulose nanofibrils with the SnO2 nanoparticles during cellulose production. The resulting SnO2@PBC composite presents highly stable capacity retention of around400 mAh g^-1 capacities at C/10 current density over 50 numbers of cycles.