Pollen morphology of six tree species belonging to four genera in Juglandaceae was observed by scanning electron microscope. The results show that pollens of six tree species are all single grain with medium size, the exine ornamentation is densely distributed by granular glyph with compound germinal apertures scattering or along equatorial; there are great differences in number of germinal apertures (average 3-22), number of germinal apertures of Juglans nigra Linn. is the most, while that of Carya illinoinensis (Wangenh.) K. Koch is the least. Polar axis length of pollen is 25. 00-37. 61μm, equatorial axis length is 21. 90 -36. 55  μm. The order of pollen size from small to big is Pterocarya stenoptera C. DC., Juglans cathayensis var. formosana (Hayata) A. M. Lu et R. H. Chang, Cyclocarya paliurus (Batal.) Iljinsk., J. nigra, J. regia Linn. and C. illinoinensis. Pollen shape of C. paliurus and P. stenoptera is flat pentagonal and flat polygonal, respectively, while that of other four tree species is flat spheroid. According to pollen size, exine ornamentation and germinal aperture morphology, evolutionary relationships of six tree species are discussed.