Many first-time parents have a question: Why is the first stool of a newborn baby dark green? Generally speaking, the first stool or the first few stools of a baby are called meconium, and the nature of meconium is slightly different from the stool of a normal baby, which is dark green and sticky in nature. There is a close relationship between the stool characteristics of infants and the intestinal flora. Most newborns pass meconium around 10 hours after birth, which is dark green, thick and odorless, due to the composition of meconium. The meconium of newborns is composed of intestinal secretions, shed intestinal mucosal cells, bile, intestinal fluid and swallowed amniotic fluid, and the color of the meconium is presented by these components. The feces that is excreted 2-3 days after birth gradually becomes infant feces, and the nature of infant feces varies with different breastfeeding practices. In the case of exclusively breastfed children, the stool is golden yellow, soft and even in texture, containing more water, with a fine paste, small particles of milk, and a sour odor, and the number of bowel movements can reach 3-6 times a day or more, and decreases after the first month. The stool of cow’s milk-fed infants is dry, yellowish, more voluminous, containing more lumpy particles, heavier odor, 1-2 times a day, and more prone to constipation. Formula-fed infants have stools closer to those of breastfed infants. After the addition of complementary foods, the infant’s stool is gradually close to that of adults.