An aspect of the present application provides a separator comprising a porous substrate, and a first coating layer disposed on at least one surface of the porous substrate and comprising an inorganic particle and a binder. The first coating layer comprises a first region and a second region, the first coating layer in the first region comprises a first thickness, and the first coating layer in the second region comprises a second thickness; the first thickness is greater than the second thickness, and the area in the second region is greater than the area in the first region. Another aspect of the present application provides a lithium ion battery comprising a positive electrode, a negative electrode and the above separator. The purpose of the present application is to provide a separator having an increased thickness in a partial coating layer and a lithium ion battery comprising the above separator.