Purpose: To assess the efficacy of motivational interviewing in conjuction with a caries risk assessment (MICRA) programme to improve the dental health status of preschool children. Materials and Methods: A randomised controlled trial was conducted among 214 parents or caregivers and their children at Health Centre 54, Bangkok, Thailand, from September 2015 to February 2016. The participants were randomised to the intervention and the control groups (107 participants per group). At baseline, the intervention group received a caries risk assessment, individual counseling by using motivational interviewing, and oral hygiene instruction. The intervention group received reinforcement education and individual counseling by motivational interviewing every 3 months. The control group received a routine programme. Participants were assessed at baseline, 3 months, and 6 months for plaque index and caries. The data were analysed by using descriptive statistics, the chi-squared test, Fisher's exact test, t-test, repeated-measures ANOVA, and negative binomial distribution. Results: After the 6-month follow-up, participants in the intervention group had a significantly lower plaque index, non-cavitated plus cavitated carious lesions, and cavitated carious lesions when compared to the control group. The intervention group had a lower caries incidence, non-cavitated plus cavitated carious lesions (1.81 times) and cavitated carious lesions (2.04 times) than the control group. Conclusion: The combination of motivational interviewing and caries risk assessment in one programme decreased early childhood caries in preschool children. It is not known whether the effects are due to the motivational interviewing, the caries risk assessment, or the combination of both. Keywords: caries risk assessment, dental health status, motivational interviewing, preschool children