A lumbar support assembly disposed on a seat back frame within a vehicle seat and configured to support the back and waist regions of a passenger, the lumbar support assembly comprising: a fixing wire configured to be disposed on the seat back frame; a comfort mat provided with an upper end disposed on a cross wire combined with an upper end of the fixing wire so as to be rotatable and configured to support the back and waist regions of the passenger; a rotating device disposed on the fixing wire and rotating a lower end of the comfort mat toward the back region of the passenger; and an operating device disposed on the fixing wire and transforming the rotating device to protrude toward the comfort mat, wherein the rotating device includes: an upper plate combined with the fixing wire so as to be movable in a length direction; a lower plate separated from the upper plate under a condition that the operating device is interposed therebetween and combined with the fixing wire so as to be movable in the length direction; and a support mat provided with a first end hinged to the upper plate and a second end hinged to the lower plate so as to support the lower end of the comfort mat at a rear of the comfort mat, characterized in that the operating device includes: a first base plate provided with both ends combined with the fixing wire so as to be movable in the length direction; a driving motor disposed at one side of the first base plate and rotating a spindle shaft; the spindle shaft located on the first base plate so as to be rotatable on its axis and combined with the driving motor; a pair of spindle nuts separated from each other on the spindle shaft and rectilinearly moving in opposite directions during rotation of the spindle shaft; a pair of upper link wires combined between the pair of spindle nuts and the upper plate; and a pair of lower link wires combined between the pair of spindle nuts and the lower plate. a fixing wire configured to be disposed on the seat back frame; a comfort mat provided with an upper end disposed on a cross wire combined with an upper end of the fixing wire so as to be rotatable and configured to support the back and waist regions of the passenger; a rotating device disposed on the fixing wire and rotating a lower end of the comfort mat toward the back region of the passenger; and an operating device disposed on the fixing wire and transforming the rotating device to protrude toward the comfort mat, an upper plate combined with the fixing wire so as to be movable in a length direction; a lower plate separated from the upper plate under a condition that the operating device is interposed therebetween and combined with the fixing wire so as to be movable in the length direction; and a support mat provided with a first end hinged to the upper plate and a second end hinged to the lower plate so as to support the lower end of the comfort mat at a rear of the comfort mat, a first base plate provided with both ends combined with the fixing wire so as to be movable in the length direction; a driving motor disposed at one side of the first base plate and rotating a spindle shaft; the spindle shaft located on the first base plate so as to be rotatable on its axis and combined with the driving motor; a pair of spindle nuts separated from each other on the spindle shaft and rectilinearly moving in opposite directions during rotation of the spindle shaft; a pair of upper link wires combined between the pair of spindle nuts and the upper plate; and a pair of lower link wires combined between the pair of spindle nuts and the lower plate.