The objective of this research is to systematically investigate the quenching characteristics of a hot sphere in nanofluids. The experiments are carried out with a small (9.5 mm) stainless steel sphere with initial temperatures near 1000 °C. Alumina nanofluids and deionized water are tested at low volume concentrations (less than 0.1 % by volume) and saturated conditions (100°C). The results show that the quenching behavior in nanofluids is nearly identical to that in pure water. Moreover it is found that some nanoparticles accumulate on the sphere surface during the quenching process. Such accumulation of nanoparticles on the surface promotes the destabilization of the vapor film in subsequent quenching experiments, thus accelerating the return to nucleate boiling at higher temperature than that in the clean surface case.