The vanadium redox flow battery (VRFB) has been identified as one of the most promising candidates for large-scale energy storage systems. Nevertheless, the high capital cost, particularly the cost of electrolytes, has hindered its broad market penetration. In this work, we use abundant seawater to replace deionized water for VRFB electrolyte preparation. Testing results show that both the coulombic efficiency and capacity retention rate in the case of using seawater electrolytes are higher than using the deionized-water electrolytes, although the battery voltage efficiency slightly decreases due to the lower mass transport diffusivity of V3+ in seawater. Moreover, the solubility of vanadium sulfate in seawater increases by ∼12%. The overall cost of seawater-prepared electrolytes is cheaper by 3.6% than that of the deionized water prepared electrolytes. The results indicate that seawater offers the potential to replace deionized water as a new avenue for VRFB electrolyte preparations.