This study was designed to be a cross-sectional study of 1440 Kinh students and 718 San Diu students from 11 to 17 years of age in Vinh Phuc and Phu Tho provinces. The study objective was to determine the age of puberty of Kinh and San Diu students in these provinces. It was found that Kinh schoolgirls reach puberty at the age of 12 years, 10 months, and San Diu schoolgirls reach puberty at the age of 13 years, 4 months. Kinh students experience their first menstrual flux earlier than San Diu students (p 0.05). Kinh schoolboys reach puberty time at the age of 13 years, 5 months and San Diu reach puberty at the age of 14 years, 7 months. Kinh male students show signs of puberty earlier than San Diu male students (p 0.05). Female students attain puberty at a younger age than male students (p 0.05). Results from this study can be used as reference material and to teach about characteristic development of school age children in order to improve the quality of care, protection and education of children.