A seat bolster adjustment assembly includes a bolster moveably mounted on a seat back with a bolster adjustment mechanism adapted to adjust and control the support provided by the bolster. The bolster adjustment mechanism may be mounted on the back side of the seat back, and may include a moveable positioning member between adjacent ribs in order to form a stop limit or positioning element when contacted by the ribs. This bolster adjustment positioning mechanism may include an adjustable brace moveable toward and away from a forward edge of the bolster to thereby adjust the stiffness of the bolster.