Aunt is the common name for what is clinically known as menstruation, and menstruation in a 9-year-old girl may be a normal physiological phenomenon. Menstruation is one of the signs of maturity of female physiological functions, and the first menstruation of adolescent girls is called menarche. The age of first menstruation is usually between 13 and 14 years old, but due to individual differences, it may be as early as 11 years old or as late as 16 years old. Early or late menarche is mainly related to hereditary factors. In addition, body weight and nutrition may also affect the age of menarche. In recent years, the age of menarche has been advancing, so it may be a normal physiological phenomenon for a 9-year-old girl to menstruate. After entering puberty, parents should give their children popularization of science, eliminate their worries and low self-esteem, and choose qualified sanitary products for their children and give them enough care and attention. However, if a girl menstruates before the age of 8, it is necessary to consider precocious puberty, and need to go to the hospital in a timely manner, and actively cooperate with the doctor to intervene in the treatment.