Despite evidence supporting the importance of breastfeeding to child health, breastfeeding practices remain suboptimal in Viet Nam. There is currently little evidence on the importance of breastfeeding in the prevention of morbidity during infancy in Viet Nam. In order to provide country specific data for policy makers to support breastfeeding friendly policies and programs, analysis was undertaken on a cross-sectional dataset to investigate the association between breastfeeding practices and prevalence of diarrhea and acute respiratory infection (ARI) among infants aged 0–5 months. Early initiation of breastfeeding was associated with lower prevalence of diarrhea, while prelacteal feeding was associated with higher prevalence. Compared to infants who were exclusively breastfed, infants who were predominantly or partially breastfed were more likely to have diarrhea. Prelacteal feeding and partial breastfeeding were associated with higher prevalence of ARI. While the protective effects of exclusive breastfeeding against diarrhea declined with child age, this effect for ARI appears to have remained constant.