Thirty-two species from 17 genera were examined by scanning electron microscopy and representatives from each subfamily were examined by transmission electron microscopy. The treatment of Ulmaceae based on pollen grains is consistent with the treatment of the family presented by I. A. Grudzinskaya. Wall structure and exine sculpturing are the best diagnostic pollen characteristics for determining subfamilial affinities. The pollen morphological characteristics of the Celtidoideae are more like those of Moraceae than of Ulmoideae, thus lending support to Grudzinskaya's suggestion that the Celtidoideae should have familial status and occupy a phylogenetically intermediate position between the Ulmaceae (Ulmoideae) and the Moraceae.