Electrohydrodynamic (EHD) has been used widely as an active method for enhancing heat transfer. It protects environmental issues and energy sources. One of its applications is in condensation of vapor. Existence of non-condensable gas in condensation system is one of the most important parameters that affects condensation heat transfer coefficient. In this thesis effects of EHD on a laboratory scale condensation system, containing a non-condensable gas has studied. Effects of various non-condensable gas concentration, applied electrical field, and electrode diameter on condensation have evaluated. In this experimental study, a horizontal condenser for condensation of R-134a refrigerant in presence of air as a non-condensable gas has been used. Experimental results show that application of electrical field enhancing heat transfer coefficient. Also presence of the non-condensable gas in condensing vapor has reduced the coefficient, which this issue is in competition with applied electrical field. It is due to variation of boundary layer thickness in heat transferring area. Experimental results show that in absence of non-condensable gas, the condensation heat transfer is enhanced by 85% with implementation of a 12mm electrode diameter and application of 8kV voltage. But in the same system and in presence of the non-condensable gas with volumetric concentration of about 25%, heat transfer coefficient is reduced more than 50%. However it must be notified that application of EHD always enhances condensation heat transfer rate, even in presence of non-condensable gas with various concentrations.