A separator for an electrochemical device, including: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate and containing a plurality of microcapsules and a binder polymer positioned on the whole or a part of the surface of the microcapsules to connect and fix the microcapsules with one another, wherein the microcapsules include metal hydroxide particles, and capsule coating layer surrounding each surface of the metal hydroxide particles. An electrochemical device including the separator, and the microcapsules are also provided. The microcapsules and separator show excellent flame resistance and can reduce degradation of battery performance caused by water adsorbability of the plurality of a metal hydroxide particle.