The heat flux in the divertor target is one of the most crucial problems for a fusion reactor. This problem is more severe in a spherical tokamak (ST) reactor because it is more compact. This paper proposes a liquid lithium divertor system to solve this problem. The heat coming from the fusion plasma along the divertor leg is removed by evaporation of lithium. The lithium vapor is condensed on the wall, and the heat is transferred to the coolant that drives power generator. Narrow slit along the divertor leg and the differential evacuation chamber reduces leakage of lithium vapor to the plasma chamber.