Disclosed are a separator and an electrochemical device comprising the same, the separator comprising: a porous substrate having a plurality of pores; and a porous coating layer formed on at least one surface of the porous substrate or at least one surface of the porous substrate and a portion of the pore, the porous coating layer containing a plurality of inorganic particles and a binder polymer disposed on a part or the entirety of a surface of the inorganic particle to connect and fix the inorganic particles, wherein the inorganic particle comprises an alumina particle and an aluminum hydroxide particle having a smaller average particle diameter than the alumina particle.