Children malnutrition is still an important public health problem in Vietnam currently. This study aims to assess the situation of stunting malnutrition in Mong ethnic children under 5 years old and identify some related factors. A cross-sectional descriptive study was conducted on 930 Mong ethnic children and 930 mothers in Can Ty and Lung Tam communes, Quan Ba ​​district, Ha Giang province. Results show that the rate of general malnutrition was 50.4%, of which stunting was 45.1%; underweight was 24.1% and wasting was 8.2% and. The rate of stunting malnutrition in children ≤ 12 months was 39.1%; 13 - 24 months was 32.0%; 25 - 36 months 42.3%; 37 - 48 months 50.3% and 49-60 months 62.8%. There is relationship between family economy, mother education level, mother's marriage aged under 18 years old, mother inbreeding marriage, mother gaining < 10 kg during pregnancy, normal delivery, crowed children, breastfeeding time after delivery, weaning time, low birth weight babies, frequent illnesses and not fully vaccinated with stunting malnutrition in Mong ethnic children (p <0.05). Thus, the rate of stunting malnutrition in Mong ethnic children under 5 years old is still high and is associated with many factors related to customs, practices and behaviors.