With the growing demand for sustainable energy technologies, ionic thermocells have attracted increasing attention for their potential in harvesting low-grade heat through direct thermal-to-electric energy conversion. Among the key performance metrics, the effective thermal conductivity (κ_eff) plays a crucial role in maintaining internal temperature gradients and enhancing overall energy conversion efficiency of thermocells. However, compared to the extensively studied thermopower (S_tg) and electrical conductivity (σ), κ_eff has received relatively little systematic attention. This review summarizes recent advances in the regulation of thermal conductivity in ionic thermocells, focusing on its crucial role in thermoelectric performance. We discuss the influence of electrode materials, electrolyte compositions, and device architectures on heat transport, and highlight representative strategies involving materials engineering and structural design to optimize the synergy between thermal conduction and ionic conduction. Finally, we outline future directions such as material optimization, interface engineering, and improved thermal characterization techniques, to facilitate the development of next-generation high-performance thermocells.