This study reports the first-recorded presence of the Korean rockfish (Sebastes schlegelii) in the Sea of Marmara, signifying a notable geographical expansion beyond its natural range. The sampled male specimen, with a total length of 27.5 cm and a weight of 459.20 g, aligns with known size patterns observed in the Black Sea, suggesting a consistent trend. The unexpected presence of the species in the Sea of Marmara raises intriguing questions about its potential spread in the broader Mediterranean Sea basin. The adaptability of the Sebastes schlegelii to diverse environmental conditions underscores its ecological resilience. The study emphasizes the need for careful monitoring and management due to potential threats posed by invasive species, especially considering the vulnerabilities of the Sea of Marmara to climate change