A rotary knob assembly capable of up-and-down motion is provided. The rotary knob assembly includes a lower case with an oil damper; a rotary sleeve rotatably disposed in the lower case with a connecting hole; a slide cam that moves linearly with respect to the lower case with a pair of cam grooves and a sleeve hole; an elastic member disposed between the slide cam and the lower case; an up-and-down moving sleeve that moves up and down with respect to the rotary sleeve with a pair of up-and-down cams inserted in the pair of cam grooves of the slide cam; a rotary knob that is rotatably connected to the up-and-down moving sleeve; and an upper case connected to the lower case to limit vertical movement of the rotary knob, wherein a moving speed of the slide cam is controlled by the oil damper.