A hydrothermally synthesized tin (IV) sulfide electrode was examined for use as a negative electrode in sodium ion batteries. Using ex-situ XRD and electrochemical analysis, the sodiation mechanism of tin (IV) sulfide was clarified, which revealed that the typical conversion reaction-coupled alloying reaction happened during sodiation with a high reversible capacity (similar to 640 mA h g(-1)). Also, the improved cycleability was observed in the tin (IV) sulfide electrode when compared with tin metal electrode. From comparison of quasi-open-circuit voltages at the 20th de-sodiated electrode, it was revealed that sodium trapping was considerably suppressed by sulfide formation with tin.