A rack-mounted KVM module is configured for a server rack. An L-shaped supporting frame, which has a vertical plane and a horizontal plane, is coupled to the sever rack. A flat panel display is coupled to the vertical sliding rail to move along the L-shaped supporting frame horizontally. A keyboard module is coupled to the horizontal sliding rail to move along the L-shaped supporting frame horizontally. A positioning mechanism is disposed in the horizontal sliding rail. The positioning mechanism consists mainly of an outer rail, an inner rail, a link bracket, a latch and a positioning switch. The latch is swiveled to engage a notch of the latch in a block portion of the outer rail or to remove the notch thereof from the block portion to respectively lock or unlock a fixed position when the link bracket is slid along the inner rail by moving the positioning switch.