To provide a hair extension which allows an easy attachment operation to a wearer's hair while reducing the size of the overall structure, and a method for attaching the same.

A hair extension includes: two flat plate-like fixed portions 11, 21 to which one end sides of a plurality of imitation hairs are fixed in a bundled manner by an adhesive; imitation hair suspended portions 12, 22 which are extended from the fixed portions respectively; and adhesive layers 13, 23 provided on one surface side of the fixed portions respectively. A cutout 30 is formed in a position including a border line B at which the two fixed portions are connected to each other.