A porous membrane of carboxymethyl cellulose (CMC) from natural macromolecule as a host of a gel polymer electrolyte for lithium ion batteries is reported. It is prepared, for the first time, by a simple non-solvent evaporation method and its porous structure is fine-adjusted by varying the composition ratio of the solvent and non-solvent mixture. The electrolyte uptake of the porous membrane based on CMC is 75.9%. The ionic conductivity of the as-prepared gel membrane saturated with 1 mol L−1 LiPF6 electrolyte at room temperature can be up to 0.48 mS cm−1. Moreover, the lithium ion transference in the gel membrane at room temperature is as high as 0.46, much higher than 0.27 for the commercial separator Celgard 2730. When evaluated by using LiFePO4 cathode, the prepared gel membrane exhibits very good electrochemical performance including higher reversible capacity, better rate capability and good cycling behaviour. The obtained results suggest that this porous polymer membrane shows great attraction to the lithium ion batteries requiring high safety, low cost and environmental friendliness.