The Oriental stork (Ciconia boyciana), an endangered species, faces significant threats despite extensive conservation efforts aimed at their reintroduction and long-term survival in South Korea. Understanding the primary causes of mortality and identifying predominant pathological lesions are crucial for enhancing these efforts. This study aimed to investigate the causes of unexplained mortality in Oriental storks between 2019 and 2023 through comprehensive postmortem examinations. Twelve storks, including both wild and captive birds, classified as “unknown“ deaths, were examined. The results revealed that parasitic infections, particularly in wild storks, were frequently observed (41.7%). Additionally, gastrointestinal obstruction due to the ingestion of foreign materials was identified in a wild stork, highlighting the impact of environmental pollution. Despite the prevalence of inflammatory lesions in liver (58.3%), no cases of hepatitis were confirmed, except for one case of liver rupture in a wild stork. Notably, three nestling death cases from a single litter of captive storks suggested potential parental infanticide or lack of parental care. The overall results highlight the importance of addressing parasitic infections and environmental risks to improve the survival of wild Oriental storks, and emphasize the need for effective management in breeding facilities. Continuous monitoring and pathological evaluations for mortality cases are essential for understanding disease trends and developing adaptive conservation strategies to ensure the long-term preservation of this endangered species.