The diagnostic performance of a commercially available ELISA IgG antibody test for Orthoflavivirus nilense (ONV, formerly West Nile Virus) was evaluated using the virus neutralization (VN) test as the reference method. A total of 494 previously collected human serum samples were analyzed. Of the 40 ELISA IgG antibody positive samples, 38 were confirmed by VN, while VN detected 41 positive samples in total. The ELISA IgG antibody test demonstrated a sensitivity of 92.68 %, specificity of 99.56 %, positive predictive value of 95.00 %, and negative predictive value of 99.34 %, with an overall accuracy of 98.99 %. Receiver Operating Characteristic (ROC) analysis revealed a high discriminative performance (Area Under the Curve (AUC): 0.961). These results suggested that the ELISA IgG antibody test can serve as a rapid, economical, and automation-compatible screening assay for ONV antibody detection in outbreak settings and large-scale surveillance. However, due to potential cross-reactivity with antigenically related flaviviruses, all ELISA-reactive results must be confirmed by VN or plaque reduction neutralization test (PRNT) in compliance with World Organisation for Animal Health (WOAH) guidance to ensure virus-type–specific antibody identification.