The suppression effect of ultrafine mists on methane/air explosions with methane concentrations of 6.5%, 8%, 9.5%, 11%, and 13.5% were experimentally studied in a closed visual vessel. Ultrafine water/NaCl solution mist as well as pure water mist was adopted and the droplet sizes of mists were measured by phase doppler particle analyzer (PDPA). A high speed camera was used to record the flame evolution processes. In contrast to pure water mist, the flame propagation speed, the maximum explosion overpressure (Delta P-max), and the maximum pressure rising rate ((dP/dt)(max)),) decreased significantly, with the "tulip" flame disappearing and the flame getting brighter. The results show that the suppressing effect on methane explosion by ultrafine water/NaCl solution mist is influenced by the mist amount and methane concentration. With the increase of the mist amount, the pressure, and the flame speed both descended significantly. And when the mist amount reached 74.08 g/m(3) and 37.04 g/m(3), the flames of 6.5% and 13.5% methane explosions can be absolutely suppressed, respectively. All of results indicate that addition of NaCl can improve the suppression effect of ultrafine pure water mist on the methane explosions, and the suppression effect is considered due to the combination effect of physical and chemical inhibitions. (C) 2014 Elsevier B.V. All rights reserved.