Na-alginate as a binder in an aqueous solvent has been applied in the preparation of sulfur cathodes for lithium-sulfur batteries. Their electrochemical performances have been investigated by a charge-discharge cycle test and electrochemical impedance spectroscopy (EIS). The EIS tests indicated that the alginate sulfur cathode had lower resistance and better kinetic characteristics than those of the poly(vinylidene fluoride) (PVDF) sulfur cathode using PVDF as a binder in a N-methy-2-pyrrolidone (NMP) solvent. The charge-discharge tests showed that the discharge capacity and the capacity retention rate of Na-alginate sulfur cathode were 508 mAh·g−1 and 65.4% at the 50th cycle with a current density of 335 mA·g−1. Compared with PVDF sulfur cathode, the alginate sulfur cathode showed a remarkably better cycle performance. These results show that the alginate binder has promising potential for lithium-sulfur battery applications.