Background: Despite the success of National Action Plan on Nutrition program in reducing malnutrition among children under 5 years old in Vietnamin recent years, the rate of malnutrition inVietnamremains higher than that rate in other surrounding countries. The rate is especially high in mountainous areas. This study aims to explore the association between the mother’s nutrition care practice and the nutritional status of their children. Methods: 400 Children under 5 years of age and their mothers from Thanh Hoa—a Northern Province of Vietnam were included in this survey. Weight and height of the children were measured. Information related to the mother’s knowledge and practices pertaining to child health care and nutrition was collected. Results: The malnutrition rate was 29.3% by weight for age score (WAZ), 28.3% by height for age score (HAZ) and 10.0% by weight for height score (WHZ). 27.3% of mothers discarded the colostrum milk. 21.3% of children were fed with chewing rice before breastfeeding. Exclusive breastfeeding up to four months was 17.8% and exclusive breastfeeding rates for 6 months or more was 8.6%. Weaning practice before four months of age was 53.7%. There was an association between malnutrition with mother’s ethnic group, and the frequency of consumption of protein rich food. Conclusion: Malnutrition of ethnic minority children under five years of age is still a public health problem in the central mountainous areas ofVietnam. Inappropriate breastfeeding and weaning practice among ethnic minority women were associated with this high rate. Further effort should continue to improve the nutrition status of ethnic minority children under 5 years of age. Customized, culturally adapted interventions for ethnic minority women to strengthen their nutrition care knowledge, attitude and practice, especially breastfeeding and weaning practice are the key to achieving better nutrition status of their children.