Pathological findings of leucocytozoonosis naturally occurred in Korea are described. Most of the affected chickens showed paleness of comb and wattle, egg drop, approximately 20 to 30% mortality, green diarrhea, anorexia and weakness. On the blood smear merozoits and gametocytes were detected. At necropsy, petechial and ecchymotic hemorrhages in liver, kidney, heart, muscle, and splenomegaly were frequently observed. Microscopically schizonts with fine granular merozoits were often detected in kidney, intestine, brain, lung, myocardium, muscle, liver with cenrilobular fatty change, and spleen.