Development process a important issue of development in children. There are many factors that influenced the development of children's teeth. This study was conducted to find somes affect factors on teething age of 1444 healthy children with age from 6 months to 42 months in nursery school in Hanoi that were randomly selected during the period from 01/10/2010 to 15/04/2011. Results showed that 'children living in Hanoi city had an eruption of primary teeth (average 25 months) earlier than children living in the suburbs (average age 27). The low birth weight infants and age of eruption of primary teeth was later than normal birth weight babies. Average age of primary teeth and the average age of the end teething infants who received additional vitamin D and canxium or vitamin D alone only were earlier than infants not added (p 0.05). The average age of the end teething babies who had sunbathing or live in places with full light was earlier than other group (p 0.01). In conclusion, the affect factors of average age of primary teeth were birth weight, additional vitamin D, canxium. The affect factors of average age of the end teething were geography, birth weight, the baby early complementary feeding, the supplements of vitamin D and canxium for children, sunbathing, sunlight in accommodation.