Pillow which can be adjusted in size according to the need of a user without changing the shape when the user changes a posture

The invention relates to a pillow, including a pillow cover and a pillow core. The pillow core includes a plurality of rolling columns accommodated in the pillow cover, wherein each of the rolling columns is formed by wrapping a sheet made of an elastic material around a central axis. Therefore, the pillow of the invention can be adjusted in size according to the need of a user without using a plurality of molds, and the shape thereof will not be changed when the user changes a posture, which can reduce the manufacturing cost and avoid wasting the earth resources. The user can even adjust the arrangement direction and position of the rolling columns so as to change the supporting effect.