Purpose: The aim of this study was to identify the effect of an observation window (OW) at peripheral intravenous (IV) catheter sites on early detection of IV infiltration among hospitalized children. Methods: This was a retrospective observational study with history control group design. Participants were children who had IV infiltration after peripheral catheterization when hospitalized from January to May, 2014 and January to May, 2015 at a children’s hospital located in Yangsan city, Korea. The 193 patients, who were hospitalized from January to May, 2014 formed the control group and did not have OW, and the 167 patients, who were hospitalized from January to May, 2015 formed the window group and had OW. Data were analyzed using χ2-test, independent samples t-test and multiple logistic regression. Results: First stage IV infiltration was 39.5% for the window group and 25.9% for the control group, which was significantly different (p =.007). The likelihood of 2nd stage and above IV infiltration decreased by 44% in the window group, which was significantly different (p =.014). Conclusion: OW at the peripheral IV catheter site was found to be an effective measure in early recognition of IV infiltration. Considering the effect of OW, we recommend that nurses should make an OW with transparent dressing during stabilization of the IV catheter site in hospitalized children in clinical settings.