Disclosed is a separator containing a porous polymer substrate and an inorganic particle layer formed on at least one surface of the porous polymer substrate, and the separator has increased insolubility for an electrolyte and enhanced dimensional stability at high temperatures, therefore, short circuit between a cathode and an anode may be suppressed even when an electrochemical device is overheated, and high temperature cycle characteristics of the electrochemical device are enhanced. In addition, discharge characteristics are improved due to an ion conductance enhancement, since the impregnation of the separator for the electrolyte increases. Therefore, the separator according to the present invention is suited for electrochemical devices that require heat resistance, in particular, for lithium secondary batteries for electric vehicles, since, while the separator according to the present invention has excellent heat resistance, an electrochemical device that includes the separator gives equal performance in electrochemical properties when compared to existing separators.