An undermount drawer slide includes a first rail and a second rail slidable linearly with respect to the first rail. The first rail has a first wall perpendicular to a reference level, and includes a first and a second installation sections. The first installation section has a first vertical distance with respect to the reference level. The second installation section has a second vertical distance with respect to the reference level. The first vertical distance is different from the second vertical distance to form a height difference. The second rail includes a top wall and a protrusion protruding from the top wall. The protrusion has a height measured from the top wall which is substantially equal to the height difference. The protrusion is adapted to hold against a bottom of a drawer for keeping a front panel of the drawer in a level status with respect to a cabinet.