Abstract: The present invention relates to a mobile air conditioner which comprises an insulated housing having a cooled air outlet and a heated air outlet, an evaporator located in the said housing, a condenser, an electrical fan having an air chamber, and a reservoir for collecting condensed water formed on the evaporator. The evaporator is located between the air chamber and cooled air outlet; while the condenser is located between the air chamber and heated air outlet. The cavity of the said reservoir is in fluid connection with a drain channel which has a drain meatus located in the air-discharge passage extended from the air outlet of the air chamber to the condenser. The condensed water from the reservoir to the drain channel can be atomized into tiny drops by rapid air flow from the air chamber. The tiny drops are blown through the drain channel onto the condenser for being heated and onto the evaporator for being cooled, then flowing into the reservoir at last.