This paper describes the heat transfer in intermediate heat exchangers (IHXs) of liquid-metal-cooled fast reactors when the flow rate is low, such as under natural-circulation conditions. Although empirical correlations of heat transfer coefficients for IHXs were derived using test data of the fast reactors Monju and Joyo and of a 50-MW steam generator facility, the measured heat transfer coefficient was very low compared to the well-known correlation for liquid metals proposed by Seban and Shimazaki. The heat conduction (HC) in IHX is discussed as a possible cause of the low Nusselt number. However, the present results show that HC is not significant under natural-circulation conditions, and the HC term in the energy equation can be neglected in the one-dimensional plant dynamics calculation. Simulations relating natural-circulation transients tested at the Monju reactor were conducted using the NETFLOW++ code with the proposed empirical correlations. Good agreement was obtained for long-term behavior.