Published studies on the diet of the Eurasian eagle owl (Bubo bubo) in Türkiye are limited to the eastern and central parts of the country. This study presents the diet composition of a single pair of eagle owl in the breeding season in Northwestern Türkiye. In total, 91 pellets of B. bubo were collected in Bolu Province. They contained 949 prey items of 18 prey species belonging to the orders Rodentia, Eulipotyphla, and Carnivora, class Mammalia and eight species belonging to the order Passeriformes, class Aves. The owl's diet was mostly composed of rodents (94.62%). Microtus hartingi, Microtus subterraneus, and Sciurus anomalus were detected in the diet of Bubo bubo in Türkiye for the first time. In addition, a specimen of Mustela nivalis was recorded in Bubo bubo pellets for the first time in Northwestern Türkiye. Niche breadth, Shannon-Wiener, and Simpson indices were calculated and found to be 6.69, 2.23, and 0.85 respectively. The estimated species richness (Chao1) of eagle owl prey was 30.9. The average prey number per pellet was 10.42 ± 5.76. The predominant species in the diet of Bubo bubo were Microtus mystacinus, Cricetulus migratorius, and Microtus subterraneus. Detailed comparison with other eagle owl prey data collected across Türkiye is also presented.