The separator for an electrochemical device of the present invention includes inorganic fine particles and a fibrous material or microporous film. Primary particles of the inorganic fine particles can be approximated to a geometric shape, and a difference between a theoretical specific surface area and an actual specific surface area of the inorganic fine particles is within ±15% relative to the theoretical specific surface area, where the theoretical specific surface area of the inorganic fine particles is calculated from a surface area, a volume and a true density of the primary particles of the inorganic fine particles, which are determined through approximation of the primary particles of the inorganic fine particles to the geometric shape, and the actual specific surface area of the inorganic fine particles is measured by the BET method.