Repeated mouth ulcers in children are not necessarily a precursor to leukemia. Repeated mouth ulcers are clinically known as recurrent aphthous ulcers, which may be related to infection, endocrine, and environment. Repeated mouth ulcers are one of the typical clinical symptoms of leukemia, but it can not be said that repeated mouth ulcers are the precursor of leukemia. Infection factors: children’s low immunity makes them susceptible to infections by bacteria and other pathogenic microorganisms. Infections can cause the immune balance of the oral cavity to be disrupted, which in turn leads to recurrent mouth ulcers. Environmental factors: including psychological environment, living and working environment and social environment. Patients tend to develop the disease under stress, emotional fluctuations, poor sleep and so on. Endocrine: In addition there are some studies that some adolescent female babies with recurrent mouth ulcers are related to the menstrual cycle. If the baby repeated mouth ulcers, parents are advised to take the baby to the hospital stomatology department in time, under the guidance of the doctor to be targeted treatment.