Air conditioner is provided that may include a case having an inlet and an outlet provided below the inlet, a heat exchanger configured to heat exchange external air introduced into the case through the inlet, a blower fan disposed below the heat exchanger and configured to be rotated by a rotational shaft formed in a lateral direction so as to send air inside the case from the inlet to the outlet, a lower guide that guides air, which is blown toward a lower side of the blower fan by the blower fan, to the outlet, an upper guide spaced apart from the lower guide to form a discharge passage with the lower guide, and a sterilization device disposed at one side of the lower guide and having a sterilization lamp configured to emit ultraviolet light toward the blower fan. A lower end of the sterilization lamp may be disposed lower than an upper surface of the lower guide.