Nine-month-old baby is thin to take the following measures: First, you should take your child to a pediatric gastroenterology clinic to check the cause, for the cause of the examination, treatment is the main thing. Second, most of them are due to insufficient energy intake, such as breast milk, milk not enough, which may cause the child’s digestion, absorption function is poor, you can give the child to take probiotics or eliminate food to strengthen the spleen and stomach type of Chinese medicine to regulate the gastrointestinal function. Third, some children may have micronutrient deficiencies, such as zinc deficiency, iron deficiency children are prone to thin, you can properly supplement zinc and iron supplements. Fourth, some children are thin because they have chronic infectious diseases, such as chronic diarrhea, milk protein allergy, lactose intolerance, etc. This situation should be actively cured. You can replace milk protein allergy with deeply hydrolyzed protein milk powder or completely hydrolyzed protein milk powder, lactose intolerance with lactase or lactose-free milk powder, and chronic enteritis with a pediatric gastroenterology clinic for anti-infection treatment for the cause of the infection.