This study was carried out to determine the percentages of both leukocyte types and lymphocytes with alpha-naphthyl acetate esterase (ANAE) positivity in the peripheral blood of young and adult pheasants (Phasianus colchicus). For this purpose, heparinised (10 IU heparine/mL blood, Liquenine, Roche) peripheral blood samples of 11 young and 11 adult pheasants were used. In the young pheasants, the percentages of lymphocytes, heterophils, monocytes, eosinophils and basophils were 56,00%, 30,09%, 7,45%, 4,64%, 1,81% respectively and ANAE-positive lymphocyte rate was 36,82%, whereas in the adults the values were found as 52,91%, 41,09%, 2,81%, 2,00% and 1,18% for lymphocytes, heterophils, monocytes, eosinophils and basophils respectively. ANAE-positive lymphocyte rate was 33,73% in the adult pheasants. Except for the percentages of the peripheral blood lymphocytes, the differences between the other values were statistically important (P<0,05).