Introduction: ARI (Acute Respiratory Infection) is one of the main causes of death among children under five in many countries worldwide. In Indonesia, 10% of ARI cases occur in East Nusa Tenggara, which is the highest prevalence of ARI in this country, with 90% of them leading to under-five mortality. There are various factors that cause the prevalence of ARI. In East Nusa Tenggara itself, environmental factors are suspected to be the risk factors for this disease. This study aims to analyse the association between environmental factors and the incidence of ARI among children under five years old in East Nusa Tenggara. Methods: A cross-sectional study was conducted by analysing secondary data sets obtained from DHS, with a total of 337 subjects examined in this study. Multivariate logistic regression was applied to investigate the association between ARI and various environmental factors. Results: This study found that the prevalence of ARI among children under five years old in East Nusa Tenggara was 9.04% of all subjects. ARI was significantly associated with the types of residence (OR 2.2, 95%CI 1.1-4.3) and passive smoking status (OR 4.7, 95%CI 1.8-12.4) as its risk factors. In addition, there was strong association between ARI and the types of roof (OR 3.3, 95%CI 1.3-8.9) as its protective factor. Conclusion: Based on the findings of this study, it can be concluded that the incidence of ARI in children under five years old was closely associated with residential area, smoke exposure, and roof materials.