Survey on 117 children aged 6-12 at the Birla children's village in Hanoi aims to: definition of first permanent molar pit and fissure decay rate in 6-12 years old children by conventional clinical examination under index ICDAS. Research methodology: cross- sectional descriptive research. Results: the rate of pit and fissure decay of first permanent molar is 39.32 percent the rat (the chi/den aged 6-9 years old are 33.33 percent, 9-12-year-old group are 40.86 percent). The rate of the 16 is 11.11 percent, the 26 is 15.38 percent, the 36 is 24.79 percent and the 46 is 33.33 percent. Conclusion: the pit and fissure decay of first permanent molar is high and the highest is in the 46 and the lowest is in the 16. The rate of mandibular first permanent molar decay is increase with age.