The asymmetric unit of the title organic–inorganic hybrid salt, poly[[μ4-bis(2-methyllactato)borato]sodium], [Na(C8H12BO6)]n, comprises a sodium cation and a bis(2-methyllactato)borate anion. The sodium cation exhibits a [4 + 1] coordination by borate and carbonyl O atoms of the bis(2-methyllactato)borate anion, leading to a three-dimensional polymeric structure.