Purpose: To determine changes in oral health behaviour following low-cost oral health education among mother-child pairs. Materials and Methods: In this controlled trial, interviews were conducted in a random sample of mothers of 12- to 15-month-olds (N = 242) attending the vaccination offices of public health centres in Tehran, Iran, and the vaccination staff provided oral health education for the mothers belonging to two intervention groups (A and B) and a control. Groups A and B received health education, but group A additionally received two reminders during the 6-month follow-up. The control group received no health education. The mothers' oral health behaviour and practices with regard to their children were scored at baseline and at the end. Changes in these scores were recorded separately for the mothers and the children and grouped into the categories prominent, minor or no improvement. Statistical evaluation was performed with the chi-square test, ANOVA and logistic regression. Results: Prominent improvement in oral health behaviour was evident in 45% of the mothers and 66% of the children in group A, 29% of the mothers and 31% of the children in group B and in 11% of the mothers and 21% of the children in the control group (P 0.001). A prominent improvement in the mothers' practices with regard to their children was related to the mother's own behavioural improvement (OR = 1.3). The intervention was most successful in group A (OR = 5.1). Conclusion: Improvement in mothers' oral health behaviour can lead to improved health practices with regard to their children. Oral health education combined with external motivation is a valuable tool for promoting oral health behaviour in mother-child pairs. Keywords: early childhood, health behaviour, low-cost health education, mothers, oral health education