Objectives: In Wilms Tumor (WT) secondary malignancies caused by the side effects of intensive treatments remain one of the important problems. Therefore, there is a need for new studies to identify low- and high-risk groups for WT and to improve the treatment regimens of children in the low-risk group. Therefore, in our study, we aimed to determine the prognostic significance of the cyclooxygenase-2 (COX-2) biomarker in WT. Materials and Methods: Our study included 24 patients diagnosed with WT between January 2010 and December 2019. The correlation between COX-2 expression and significant prognostic parameters was investigated by studying COX-2 antibody using the immunohistochemical method. Results: COX-2 expression was observed in 22 of the patients, and the expression was more evident especially in the epithelial component. There was no significant correlation between COX-2 positivity and prognostic parameters. Conclusions: In our study, no significant relationship was found between significant prognostic parameters and COX-2 expression. We think that the COX-2 pathway is effective during the development phase of WT, since COX-2 expression was observed in almost all patients, therefore it may be beneficial to add COX-2 inhibitors to the treatment, and that a sufficient number of studies should be conducted in this respect.