Eco-friendly harnessing of both ocean chemical energy and solar energy would represent a sustainable solution for future energy conversion/storage systems, but it has been challenging to enhance the energy efficiency of such systems for practical applications. Here, we demonstrate an efficient photoelectrochemical-assisted rechargeable seawater battery. By integrating TiO2 nanostructure-based photoelectrodes with the seawater battery, we achieved significant enhancement of the voltage efficiency during the charging/discharging processes; effective photocharging with the TiO2 photoanode reduced the charging voltage to ∼2.65 V, while the heated carbon felt (HCF) cathode in the seawater battery exhibited charging/discharging voltages of ∼3.8 V and ∼2.9 V, respectively. Such a charging voltage reduction led to a voltage efficiency of ∼109%. Moreover, interestingly, we found that TiO2 nanostructures showed excellent photoelectrochemical performances in seawater in association with the efficient photocharging. As a result, the utilization of TiO2 nanostructures as photocharging/discharging electrodes provides a feasible strategy to optimize the cell configuration for highly efficient solar seawater batteries.