An experimental study concerning the frost formation in natural convection subjected to the influence of EHD is conducted. For the ambient temperature above the sub-freezing point and without the influence of EHD, water vapor deposited on the surface in the form of small droplets. A significant amount of coalescence of the small droplets is seen at the early stage of frost formation and the number of droplets increases with the relative humidity, but the size of the droplets decreases with the rise of the relative humidity. A hexagonal structure is observed as the droplet grew over a critical size (d > 80 mum). However, when the ambient temperature was below the sub-freezing temperature, the hexagonal structure was not seen because of the lack of droplets coalescence and the frost structure is comparatively uneven. With the presence of EHD, the ice column is pulled up towards the electrode and the structure is relatively skinny and fragile. The fragile structure can easily break up and fall off due to the influence of gravity. It was also found that the electric polarity plays a significant role on the frost growth. For a negative- polarity, the frost structure is thinner than for a positive polarity and the break-off frequency of the ice column is more frequently compared to a positive polarity. It is likely that this phenomenon is related to the opposite direction of the dielectrophoreic force and the electrostrictive force at a positive polarity whereas the direction of the dielectrophoreic force and the electrostrictive force are the same at a negative polarity. (C) 2004 Elsevier Ltd. All rights reserved.