Mouth ulcers are not necessarily a precursor to leukemia, caused by mouth ulcers for a variety of reasons, the more common are nervousness, fatigue, decreased immunity; there may be due to nutrition, trace element deficiencies, such as the lack of vitamin B2 or zinc, all affecting the normal metabolism of the oral mucosa, which can lead to mouth ulcers; there are also local physical, traumatic factors, such as bite wounds, burns, etc., can lead to mouth ulcers, so these are the causes of mouth ulcers, not necessarily leukemia. Mouth ulcers can also be caused by local physical and traumatic factors, such as bite wounds and burns, so these are the causes of mouth ulcers and not necessarily caused by leukemia. Leukemia belongs to the malignant tumor of hematopoietic stem cells, if leukemia, the patient’s body immune function decreases, oral ulcers may occur. Sometimes leukemia cells can form localized infiltration in the oral mucosa, which can also lead to lesions and ulcer formation in the oral cavity. Although leukemia patients can appear oral ulcers, but can not be considered oral ulcers are a precursor to leukemia, if necessary, can do routine blood, bone marrow aspiration examination, can be clear whether the combination of leukemia.