Background: The prevalence of dental caries is very high among Vietnamese children why methods and techniques for good oral hygiene behaviours therefore is very important in caries prevention. Aim: To assess oral hygiene before and after supervised tooth-brushing education in six-yearold children. Design: A pilot study with a pre-post-test design was used. Forty children, six years of age, at a primary school in Hanoi, participated in the study. The modified Bass tooth-brushing method were taught. Oral hygiene, i.e. dental plaque, was assessed on each tooth surface before the tooth-brushing education and after one week. Results: There was a distinct and significant improvement in tooth-brushing skills among sixyear- old children of both genders after the tooth-brushing education. The rate of dental plaque was reduced by 40% after the education. An improvement in cleaning could be seen on all four tooth surfaces (buccal, lingual, mesial and distal). Conclusion: School-based education in tooth-brushing technique are very effective for improving oral hygiene among six year olds.