An endometrial thickness of 11mm 5 days after menstruation is not normal. The endometrial cycle is divided into menstrual phase, proliferative phase and secretory phase. The proliferative phase of endometrium is the 5th to 14th day of menstruation, during which the endometrium proliferates from 0.5mm to 3-5mm, and it is impossible for a normal person to have an endometrium that reaches 11mm 5 days after menstruation. When the thickness of the endometrium exceeds 11mm 5 days after menstruation, there may be the possibility of endometrial exfoliation insufficiency or endometrial polyps. It is recommended to take a blood test for human chorionic gonadotropin (HCG) to rule out pregnancy. When the endometrial thickness is 11mm 5 days after menstruation, the patient should go to the hospital in time for relevant examinations, and under the guidance of professional doctors to clarify the cause of the disease and targeted treatment.