Mouth ulcers may be able to heal in three weeks, mouth ulcers need to pay attention to diet, if necessary, with the help of drugs. 1. Mouth ulcers have self-limiting characteristics, common mouth ulcers can be healed in a week or so, such as mouth ulcers are more serious, the depth of mouth ulcers reached the muscle layer, the healing time will be longer, it may take three to four weeks to heal. 2. If you want your mouth ulcers to heal within three weeks, you can drink more water, eat more fresh vegetables and fruits, pay attention to a balanced diet, eat less spicy, irritating and fried food, pay attention to maintaining adequate sleep, and enhance physical exercise. If the mouth ulcers are not healed for more than three weeks, you can use the mouth ulcers and other drugs to promote healing. It is recommended to go to a regular hospital in time to see a doctor to guide the use of medication.