Purpose: The present study sought to apply the expanded theory of planned behaviour (TPB) to the prediction of mothers' intention to brush their children's teeth and examine the mediating role of the variables of the TPB on the relationship between past behaviour and the intention. Materials and Methods: This cross-sectional study was carried out among 211 mothers with children ages 2 to 5 years. Participants completed measures of the TPB (i.e. attitude, subjective norm, perceived control and intention) and past behaviour in relation to brushing. Regression analyses were conducted to explore the predictors of mothers' intention. Mediation was assessed using Preacher and Hayes' INDIRECT.SPSS macro. Results: The TPB explained 25% of the variance in brushing intention, with attitude, subjective norms and perceived behavioural control making significant contributions. Past behaviour explained an additional 3% of the variance in intention. Analysis showed that TPB variables only partially mediate the effect of past behaviour on intention. Conclusions: Our findings revealed that mothers' intention to brush their children's teeth is under the control of both past behaviour and psychological factors. Accordingly, interventions to improve children's toothbrushing should focus on the motivational (e.g. attitude) as well as the habitual determinants (e.g. environmental cues). However, given the low explanatory power of our model, it may be necessary to incorporate other psychological and environmental variables into an explanation of the mothers' intention to brush their children's teeth. Keywords: brushing, children, oral health, past behaviour, theory of planned behaviour