To determine the effectiveness of a motivational interviewing-based educational program in reducing the number and intensity of new caries and bacterial dental plaque levels at 6 months post randomization.A randomized and single blind clinical trial in 100 schoolchildren between 6-10 years of age presenting the highest risk score of caries according to the Caries Management by Risk Assessment (CAMBRA) criteria was performed. These patients were randomized to two groups: control (in which the mothers initially received an oral prevention informative session) and experimental (in which the mothers received the initial informative session, followed by individual motivational interviewing sessions during a period of 6 months). The International Caries Detection and Assessment System (ICDAS) scores and bacterial plaque were evaluated at baseline, at 6 and 12 months.After 12 months, children in the experimental group had 2.12 ± 0.8 new caries versus 3.5 ± 0.9 in the control group (t=7.39; p<0.001). Caries in the experimental group was seen to be limited to the enamel, with a median intensity of 2 (range 0-3) versus 3 (0-6) in the control group (U=1594; p<0.0001). Bacterial plaque determined by the O'Leary index decreased in both groups; however, it decreased more in the experimental than in the control group (34.3 vs. 20.6; t=-3.12, p= 0.002) respectively.Motivational interviewing is better than traditional educational programs in preventing caries and decreasing bacterial plaque. Key words:Health educational, motivational interviewing, caries risk.