Provided are a separator having high heat resistance, a manufacturing method thereof and a secondary battery including the separator, which provides excellent dispersibility and reduced thermal shrinkage. The separator includes separator includes a porous base layer, and a coating layer formed on at least one surface of the base layer, wherein the coating layer includes inorganic particles and a binder, and the binder includes one selected from the group consisting of polyacrylic acid (PAA), polyacrylate or a mixture of polyacrylic acid (PAA) and polyacrylate, having a molecular weight of 100,000 to 1,000,000, as a first binder.