Objective: This study aimed to assess associations between sociodemographic and oral health behavioural factors with dental caries and oral health-related quality of life (OHRQoL) attributed to dental caries in a national representative sample of 12- and 15-year-old Thai children. Method: A representative subsample from the sixth Thailand National Oral Health Survey, 1,063 12-year-olds and 811 15-year-olds, completed a questionnaire on sociodemographic and behavioural information and were orally examined and interviewed about OHRQoL using the Child-OIDP or OIDP indexes. Associations of sociodemographic and behavioural factors with DMFT and Condition-Specific impacts (CS-impacts) attributed to dental caries were investigated using Chi-square tests and regressions. Results: For both groups, DMFT scores were associated with gender, geographic area and recently receiving dental treatment. Geographic area was the only sociobehavioural factor independently associated with CS-impacts. Dental caries accounted for the significant associations of sugary snacks and drinks consumption with CS-impacts. Significant associations of CS-impacts with consuming crispy snacks in 12-year-olds and fizzy drinks in 15-year-olds became non-significant when DT was entered into models. Conclusions: There were considerable geographic differences in DMFT and CS-impacts attributed to dental caries among Thai children.