Pollen morphology and ultrastructure are described for four male-fertile cultivars ('Firdola', 'Karamehmet', 'Sarialama', and 'Haciomer') and two male-sterile cultivars ('Osmanoglu' and 'Vakit Kestanesi') of chestnut (Castanea sativa Mill.) using light microscopy and both scanning and transmission electron microscopy. Pollen grains of both male-fertile and male-sterile chestnut cultivars are tricolporate, the germinal furrow extending almost the full length of the grain axis. Pollen grains have a slightly reticulate exine. Pollen grain length varied from 13.33 - 21.30 mu m, and decreased significantly in the male-sterile cultivars. Three different pollen shapes were observed among the cultivars: prolate, perprolate, and sub-prolate. The ultrastructure of the pollen grains did not differ between male-fertile and male-sterile cultivars. Intine, exine and total wall thickness (exine + intine) of pollen grains were determined as: 83.2 - 153.1 nm, 432.8 - 520.0 nm, and 516.0 - 651.6 nm, respectively; and variations were significant (P <= 0.05) among cultivars. The percentages of in vitro germination of pollen grains of male-fertile cultivars were between 11 - 78%, and the variations among cultivars were significant (P <= 0.05). The percentages of empty pollen grains observed among cultivars ranged from 3 - 32%. The correlation coefficient between the percentage of normal pollen and the germination rate was r = 0.898 (P <= 0.01).