A chair back height adjustment mechanism comprises a guide having an abutment surface at a lateral side of the guide which extends along an adjustment direction. The chair back height adjustment mechanism comprises an adjusting device supported on the guide so as to be displaceable along the adjustment direction. The adjusting device comprises a carrier, a coupling member which is moveably supported on the carrier, and a bias mechanism. The coupling member has a contact face shaped to abut on the abutment surface of the guide and a slanted face. The bias mechanism is operative to apply a force onto the slanted face to urge the contact face of the coupling member against the abutment surface of the guide.