Acute Respiratory Infection (ARI) remains a major health problem among under-five children with a relatively high incidence rate with a prevalence of 20% of global under-five mortality cases in 2024, and parents’ level of knowledge is considered an important factor influencing preventive behaviors. This study aimed to analyze the relationship between parents’ knowledge of ARI and ARI preventive behaviors among under-five children in the working area of UPTD Puskesmas III South Denpasar. This study employed an analytical correlational design with a cross-sectional approach, involving 92 parents of children aged 1–4 years selected using purposive sampling. Data were collected using questionnaires on parents’ knowledge of ARI and ARI preventive behaviors, and analyzed using univariate and bivariate analysis with the Spearman Rank test. The results showed that most respondents had a good level of knowledge regarding ARI and demonstrated good ARI preventive behaviors, representing the largest proportion among all categories. The Spearman Rank test indicated a p-value < 0.05, confirming a statistically significant relationship between parents’ knowledge of ARI and ARI preventive behaviors. The correlation coefficient value of r = 0.393 indicates a moderate category and a positive relationship with moderate strength. These findings suggest that adequate parental knowledge plays a key role in shaping preventive behaviors against ARI. In conclusion, higher parental knowledge is associated with better ARI preventive behaviors, highlighting the importance of continuous health education for parents.