Background: management and prevention of acute respiratory infections (ARI) is a worldwide problem especially in developing countries. Mothers are the caregivers of their children and thus their knowledge could be used as preventive measure for the disease. Objectives: assessing the knowledge, attitude and practice (KAP) of Saudi mothers toward ARI in children less than five years old in the Kingdom of Saudi Arabia. Methods: the study included 733 mothers admitted to a random sample of PHC from different districts of KSA. The mothers were interviewed and asked to fill up a predesigned questionnaire during the period from February 2017 to June 2017. The questionnaire comprised of 4 parts including the mothers' demographics and KAP. Results: the mean age of mothers was 41.3 years old and the duration of marriage was from 10-20 years in most of mothers (41.9%). The majority of participants had college degree (53.9%) and 44% of subjects were working mothers. Most of subjects had good knowledge about that ARI is a disease of both upper and lower respiratory infection, pneumonia as a complication of ARI, the overuse of antibiotic and bacterial resistance and cough being the most common symptom of ARI. Poor knowledge was related to the use of antibiotics and consulting a physician if children had ARI. The knowledge score of mothers was good in 46% of subjects and 54% have insufficient knowledge. The attitude and practice of mothers was poor among more than half of the participants.Conclusion: most of Saudi mothers had inadequate, knowledge, attitude and practice toward ARI. The better understanding and sufficient knowledge was significantly correlated with young ages, short duration of marriage and higher education.