A lithium secondary battery includes an electrode assembly having two electrodes and a separator interposed between the two electrodes, and a case for storing the electrode assembly, wherein the separator is formed by using a binder and a filler including a solid electrolyte having lithium ion conductivity. The lithium secondary battery has a separator and an electrolyte capable of increasing internal ion-conductivity. Also, a lithium secondary battery has a separator capable of safely preventing a short circuit between the electrodes in a possibly high temperature.