The present investigation reports the rewetting phenomenon by bottom flooding in vertical pipes using both water and nanofluid as coolant. The transient temperature response of rewetted surface indicates that rewetting takes place faster in nanofluids than in water. The effect of several parameters, including the coolant flow rate, distance from the inlet of fluid, concentration of nanoparticle loading on the rewetting characteristics, has been investigated. The rewetting velocity, for both water and nanofluid, is observed to depend strongly on the inlet coolant flow rate and initial wall temperature of the tube. The rewetting velocity is observed to follow the correlation for water proposed in an earlier work. Starting from the logic proposed in that previous report, the authors propose a correlation for predicting the rewetting velocity in nanofluids.