Abstract: During the decay heat removal, the sodium flow though wire-wrapped rod bundles is driven by the buoyancy, and its rate is low. Therefore, it is of great significance to determine the friction resistance factor of the wire-wrapped rod bundle at low velocities for the design of the passive decay heat removal system of sodium-cooled fast reactors. The friction resistance fractors in the wire-wrapped 19 and 37 rod bundles were measured using low velocity water flows with Re<1 000. The results show that the friction resistance factors of the wire-wrapped rod bundles increase rapidly with the decrease of flow rate and have an obvious increase with Reynolds number when the flow regime in the bundles starts to transition from laminar flow to turbulent flow. At low velocities, the correlation predictions about the friction resistance factors of wire-wrapped rod bundle are discovered to be smaller than those of the measurements, but the predictions about transition Reynolds numbers are observed to be larger.