OBJECTIVES: To quantify associations between behavioural determinants and antibiotic prescribing practices for acute respiratory infections (ARIs) in primary care in Vietnam. METHODS: We linked routine prescribing records with a cross-sectional prescriber survey from 112 commune health centres in northern Vietnam. Behavioural determinants derived from the survey questionnaire were mapped to the Theoretical Domains Framework (TDF), and logistic regression examined associations between each determinant with overall antibiotic prescribing and use of 'Watch' antibiotics (WHO AWaRe classification), adjusting for prescriber characteristics. RESULTS: We analysed 123,726 ARI consultations by 127 prescribers. Antibiotics were prescribed in 97.8% of visits, and 76.2% of survey respondents underestimated their own proportions. Limited access to diagnostics (42.5%) and near-weekend consultations (27.6%) were commonly reported drivers of unnecessary prescribing. Ten TDF domains were represented. High confidence in refusing antibiotic requests when not necessary (adjusted odds ratio [aOR] 0.45, 95% CI 0.22 - 0.95) and prior antimicrobial resistance (AMR) training (aOR 0.34, 0.16 - 0.70) were associated with reduced overall prescribing. For Watch antibiotics, confidence in refusing antibiotic requests (aOR 0.46, 0.25 - 0.83) and answering patient questions (aOR 0.47, 0.25 - 0.89) were associated with lower prescribing. CONCLUSION: Antibiotic prescribing for ARIs in Vietnamese primary care was almost universal, and most prescribers underestimated their own prescribing levels. Communication self-efficacy and prior AMR training were associated with prescribing outcomes. AMR strategies should combine communication-skills training, practical ARI management guidance, audit-and-feedback on individual prescribing, and access to diagnostic tools to reduce unnecessary prescribing.