Objective: Children with pneumonia need a correct position to increase their oxygen saturation and comfort level. Postural changes affect the function of the human body and disease conditions. This study aimed to identify the effect of prone and semirecumbent positions on the oxygen saturation and comfort level of children under five with pneumonia. Method: The study design was a quasi-experimental with a pre-posttest control group design. Thirty-six children with pneumonia aged 0-59 months were selected using consecutive sampling and divided into three groups: prone (n = 12), semirecumbent (n = 12), and control (n = 12). Statistical analysis was conducted using the Wilcoxon test, paired t test, and Kruskal-Wallis test. Results: A significant difference in the oxygen saturation level was found among the three groups, particularly in the semirecumbent group. No significant difference was observed on the comfort level in all groups. Conclusions: The semirecumbent position can be applied to improve the oxygenation status of children under five with pneumonia. Therefore, nurses should teach the family how to position the children with pneumonia during their hospitalization.