Abstract: The fine structures of merozoites and gametocytes of Leucocytozoon caulleryi from peripheral blood, liver, spleen and othef tissues of naturaliy infected chickens were examined under electron microscope. Results revealed that:The merozoites of Leucocytozoon caulleryi appeared to be round to oval in shape and were surrounded by two clearly marked membrances, i.e.a thin outer and a thick inner membrane. The merozoites possessed a large round to oval nucleus, a small nucleolus, numerous ribosomes,a mitochondria with tubular cristae and 1 - 2 large lipid inclusions. The micro- and macro-gametocytes were surrounded by 3-layered clearly marked membrane as in Leucocytozoon sabrazesi but in the mature gametocytes of L. caulleryi only 2-layered membrances were seen. The mature gametocytes were round or elliptical in shape and contained a nucleus, numerous ribosomes, food vacueles, lipid inclusions and endoplasmic reticulum in the cytoplasm. The microgametocytes were smaller than macroga-metocytes and possessed a large nucleus. The macrogametocytes were also easily distinguished from microgametocytes by their dark staining appearance and their well developed endoplasmic reticulum.