A latch device for a pet cage includes a latch member connected to outside of the door and includes an insertion with a hole and a lever. A positioning member includes a board fixed on the cage and located below the opening. A flexible plate extends from the board and a gap is defined between the board and the flexible plate. A tongue extends from the board and toward the flexible plate. The insertion of the latch member is inserted in the gap and the tongue is engaged with the hole to prevent the door from being lifted upward to open. The user may pull the lever to push the flexible plate away from the board to disengage the tongue from the hole so that the door can be lifted upward.