A back cushion includes an enclosure portion, a buffer portion, a filler portion and a fixing portion. The enclosure portion has a first surface/layer and a second surface/layer. The buffer portion and the filler portion are placed in the internal space of the enclosure portion. The buffer portion is in contact with the first layer and the rear surface of the filler portion is in contact with the second layer. The fixing portion is connected with the second layer of the enclosure portion. The fixing portion enables the back cushion to be attached to a suitable place of a chair or a supporting member. The buffer portion allows the back of a user can be comfortably cushioned and supported and hence injuries to his back may be avoided.