A fan assembly comprises a frame and a securing element. The frame has a first end portion, a second end portion and a middle portion. The foam securing element comprises a positioning hole having a first hole having a shape corresponding to the first end portion, a second hole having a shape corresponding to the second end portion, and a third hole having a cross section larger than that of the second hole. When the second end portion is inserted into the first hole, the second end portion and the middle portion pass through the first hole and the first end portion urges against the periphery of the second hole to receive the second end portion in the third hole. The second end portion of the frame is stopped by a periphery of the positioning hole after rotating at a predetermined angle so that the frame is positioned.