It is highly desirable to achieve optimal reproductive performance, reliable morphological and physiological basic data of the reproductive organs. Therefore, seasonal changes in serum testosterone, LH, and FSH concentrations, and morphological changes in testicular epithelial cells were studied in the Korean native pheasant throughout the annual cycle. Mature male pheasants[14-16 months after hatching] were used in this study. The general morphological changes of the epithelia of the seminiferous tubules were observed by dibasic stain, and semithin section from Epon blocks with a phase contrast microscopy. The ultrastructural changes of the the epithelia of the seminiferous tubules were investigated by ultrathin section with transmission electron microscope. The changes in the profiles of the serum FSH, LH, and testosterone concentratioins were measured by RIA[radioimmunoassay]. The results obtained are summarized as follows : 1. There was little variation in the average diameter of the seminiferous tubules from autumn[67.13+/-5.95micrometer] to winter[68.59+/-6.07micrometer], but the highest levels were reached in spring[192.78+/-41.58micrometer]. Thereafter, the diameter decreased slowly in summer[146.57+/-43.68micrometer], then decreased significantly in autumn[67.13+/-5.95micrometer]. 2. Serum testosterne concentration was low from autumn[13.+/-7.21ng/100ml] to winter[17.39+/-13.75ng/100ml], but the highest levels were reached in spring[127.72+/-66.47 ng/100ml]. Thereafter, the concentration was lowest in autumn[13.+/-7.21ng/100ml]. 3. Serum LH concentration increased slowly and linealy from autumn[5.04+/-1.04ng/100ml] to winter[6.23+/-1.08ng/100ml], but the highest levels were reached in spring[11.3+/-3.6 ng/100ml]. Thereafter, the concentration reached the lowest level in autumn[5.04+/-1.04 ng/100ml]. 4. Serum FSH concentration was low from autumn[4.65+/-0.63ng/100ml] to winter[4.2+/-0.98ng/100ml], but the highest levels were reached in spring[17.41+/-8.35ng/100ml]. Thereafter, concentration was the lowest in autumn[4.65+/-0.63ng/100ml]. 5. The seminiferous tubules showed the onset of the spermatongenic cycle in spring but the seminiferous tubules collected in summer exhibited partially degenerative changes. 6. The cytoplasmic process of Sertoli cells of the seminiferous tubules of the pheasant were collected in summer. Many vesicles and degeneratiye changes were included but many number of spermatozoa were embedded partially in the multivesicular bodies in these processes. 7. The diameter of the seminiferous tubules of the pheasant narrowed markedly in autumn, and atrophied in winter. The spermatogonia and Sertoli cells were arranged in monolayer. 8. The myelin figures in the cytoplasmic process of Sertoli cells of the seminiferous tubules of the pheasant in autumn. The nucleus of the Sertoli cells were of a round configuration elongated and oriented perpendicularly to the basement membrane. The results obtained provide basic data for reproductive physiology and are useful for studying the male genital organs of the Korean native pheasant. Structural changes of the seminiferous epithelial cells significantly and postively correlated with serum FSH, LH. The correlation of changes in the hormonal status with alterations of Sertoli cell organells precedes the breeding season.