A pedal-controlled movable bottom frame includes a frame body, two movable connecting rods and a position rod. The frame body and the movable connecting rods are respectively provided with two casters and have their ends respectively assembled with four support legs of a worktable. The position rod is assembled between the two movable connecting rods, having its intermediate portion secured with a retaining unit. A pedal is assembled on the frame body above the retaining unit, and a clasping member is provided under the pedal. The frame body and the movable connecting rods is turned downward by treading the pedal once, letting the casters support the worktable and the clasping member clasp the retaining unit. The clasping member disengages from the retaining unit by treading the pedal once again, letting the support legs support the worktable again.