A suspension for a vehicle including a strut tube; a strut rod installed so as to be movable in the strut tube; an insulator part through which an upper end of the strut rod is installed, and which includes a lower cup, an insulator body and an upper cup; and a cap member coupled to the upper cup so as to prevent penetration of foreign matters, and having a coupling structure coupled to the upper end of the strut rod. An anti-rotation structure for preventing rotation of the cap member may be provided in the cap member and the upper cup.