Abstract: The present invention discloses an automobile side back cushion, including: a mounting rod, including a first chute and a second chute disposed at an interval, and an adjusting channel disposed between the first chute and the second chute; a first side cushion and a second side cushion, which are respectively connected to two ends of the mounting rod; and a width adjusting structure, including: a first fastening frame, including at least one first inserting rod groove accommodated in the first chute and a first gear bar fixed on the outer side of the first inserting rod groove; a second fastening frame, including at least one second inserting rod groove accommodated in the second chute, and a second gear bar fixed on the outer side of the second inserting rod groove; and an adjusting gear disposed in the adjusting channel.