Newborn thumbs inward clenched fists are mostly normal physiological phenomena. When the baby is still in the mother’s womb before birth, it is the natural state of clenching the fist. Newborns are just born soon, the brain nerve has not yet matured, the power to control the muscles of the hand is relatively weak, unable to flexibly dominate the thumb extensor muscle to let the thumb open, resulting in the thumb to the palm of the hand movement, presenting the thumb inwardly withholding the rest of the four fingers wrapped in the thumb on top of the phenomenon. With the growth of the baby’s large movement, the continuous development of various systems, the brain’s innervation ability to enhance the baby’s fingers will gradually flexible, most of the thumb phenomenon will slowly disappear in about 3 months. If the newborn thumb buckle close to the palm, and more than the center line of the palm, is an abnormal phenomenon, we must consult a doctor in a timely manner to identify the causes to give symptomatic treatment, so as not to affect the normal growth and development of newborns.