To assess knowledge, practical competence and reported practices among health-care providers about antibiotics to treat acute respiratory infections in children under five in rural Vietnam. Health-care providers prescribing or dispensing western drugs for children self-completed a structured questionnaire. Recommendations concerning antibiotic use from WHO and national guidelines were used to assess the appropriateness of reported treatment of acute respiratory infections. Ninety-six per cent of 409 eligible health care providers participated. Only 27% demonstrated correct knowledge regarding the consequences of resistance. Seventy-nine per cent would use antibiotics for common colds with fever, and 21% in cases with no fever. Nineteen per cent had overall knowledge compliant with recommended guidelines. Stated antibiotic use in written scenarios for common colds (81%) was not significantly different from that for non-referral cases of pneumonia (87%). The proportion of antibiotic use in the common cold scenario was significantly lower among health-care providers who had the correct overall knowledge. According to reported symptoms from the most recent encounter with a sick child, the diseases seen were 62% mild acute respiratory infections, 19% severe, and 19% non-respiratory infections. Among those, antibiotics, most commonly beta-lactams, were used in 90%, 87% and 78% of cases, respectively. Antibiotics are often prescribed or dispensed to treat common colds. Interventions to change prescribing and dispensing practices should be developed and implemented in collaboration with local and national paediatricians. Continuous training of health-care providers, particularly drug sellers, is important.