Objectives: To determine the rate of dental and oral diseases, relative factors of Mong primary schools children in Yen Bai province. Methods: Cross-sectional and retrospective study: interview and clinical examination for 1370 Mong primary school children in age 7 - 11 of 04 primary schools: Nam Co, Pung Luong (Mu Cang Chai district), Ban Cong, Xa Ho (Tram Tau district). Results: The rate of tooth decay disease of these school children is 71,38 percent, The rate of decay is 69,64 percent, the rate of gingivitis is 50,11 percent. The average of of decay-lose-soldes index in baby-tooth is 4,07 and in older is 1,55. The index of tooth decay to be treated is 0,03. The rate of dental and oral diseases had been related to nosh habit and hygienical practice every day (there is significant difference, p0,05), related to school children knowledge (there is significant difference, p0,001), related to regular dental and oral health care (there is significant difference, p0,001). Conclusions: The rate of dental and oral diseases in Mong primary school children is very high, but examinated, treated is very low. The author recommened that: It's necessary to have curriculum for health education and health care according to the age of school children.