Objective: To evaluate the knowledge of nutrition among mothers of children less than two years of age and changes in theoretical knowledge after a nutrition course. Method: A pilot study with a pre-post-test design. Thirty mothers of children who were less than two years of age from outside Hanoi participated in the study. The mothers’ knowledge of breastfeeding, supplementary food and diet when the child was suffering from diarrhea was collected using 19 self-reported questions. A one-day nutrition course at which the mothers answered the same questions before and after the course was run. Results: All the invited mothers were included in the study. There was a lack of knowledge about breastfeeding and nutrition at baseline, but it improved after the nutrition course. The greatest improvement in knowledge related to breastfeeding less than 30 minutes after delivery, not giving milk or fruit juice instead of breast milk, increasing the frequency of breastfeeding in the event of a smaller amount of milk and knowledge about giving supplementary food after six months. Moreover, the results revealed that the mothers reported better knowledge of the consumption and frequency of more healthy food supplements. Conclusion: There was a lack of knowledge about nutrition among the mothers with children less than two years of age. The course demonstrated effectiveness in every aspect of nutritional knowledge, tested in the post-test. The findings in this study could provide important information for authorities in the health sector to improve the nutritional state of children in the community.