Background: acute respiratory infection (ARI) is an acute infection of the upper and lower respiratory tract that often occurs in toddlers. In 2018, there were 60.862 ARI cases in Kupang. In 2019, there were 2,384 ARI cases in toddlers in Puskesmas Oebobo. The average incidence of ARI in toddlers on SeptemberDecember 2019 in Puskesmas Oebobo is 642 cases. Factors related to ARI are the characteristics of toddlers including sex, low birth weight (LBW), nutritional status, immunization status and history of exclusive breastfeeding and maternal characteristics including education and mother’s knowledge. Aim: to analyze factors associated with incidence of acute respiratory infections in toddler in Puskesmas Oebobo. Research Methods: the research method is quantitative analytic with cross sectional approach. The sample in this study were mothers who had toddlers aged 0-5 years in Puskesmas Oebobo as many as 98 respondens with accidental sampling technique. The instrument in this study used a questionnaire. The analysis of the data used in this study is chi square test. Results: there is significant relationship between mother’s knowledge with the incidence of ARI in Puskesmas Oebobo (p value = 0,008). Recommendation: socialization and education about prevention of ARI is needed especially for mothers.