Abstract <p>This study provides new information on the first colonial breeding of an alien species, the cattle egret (<i>Bubulcus ibis</i>) in Mangyongdae-dong, Mangyongdae district, Pyongyang, DPR Korea. Mangyongdae forest with a total vegetation area of 112 hectares has been used as a breeding habitat for ardeid species (black-crowned night-heron <i>Nycticorax nycticorax</i>, great egret <i>Ardea modesta</i>, intermediate egret <i>Egretta intermedia</i>, little egret <i>Egretta garzetta</i>, and grey heron <i>Ardea cinerea</i>) since the 1990s. In 2024, we first found the breeding population of cattle egret <i>Bubulcus ibis</i> in a subplot of the forest in Mangyongdae. Reproductive behavior was observed from mid-May to mid-September. Nests were found in 101 trees of 16 different species. The average height of nesting trees was 11.1 ± 2.9 m. The total number of active nests was 907 and the density of nests per tree was 8.98 nests tree^–1. Mean clutch size was 2.89 ± 0.94 eggs per nest (<i>n</i> = 84), and the most common clutch size was three (50%). Mean hatch success was 2.77 ± 0.81 hatched eggs per nest (<i>n</i> = 52). This finding suggests a possibility of expansion of cattle egrets’ breeding area in the future in DPR Korea therefore a potential habitat management strategy should be developed.</p>