Abstract: Pollen gains of 33 species in 21 sections of Acer, together with two species of Dipteronia were observed by light microscope (LM) and scanning electronic microscope (SEM). The shape of pollen grains in this family varies from subspheroidal to prolate in equatorial view and is 3 - lobed circular in the poilar view. The aperture types of both species in Dipteronia are tricolporate. This type can also be found in 4 sec-tions of Acer, but most species in Acer are tricolpate. As for the pollen exine sculpture, both species in Dipteronia and most spcies in Acer are striate, but two sections in Acer are finely striate - reticulatoid or reg-ulate. By the studies of pollen morphology and other evidence, it is inferred that : (1) Sect. Palmata, Sect. Spicata and Sect. Microcarpa may be the closest groups in Acer to Dipteronia; (2) A. distalum and A. nipponicum represent two related monotypic sections; (3) The pollen of A. pseudoplatanus, which is different from other four species in Sect. Acer, is similar to that of A. sacchamm. It therefore indicates that these two species have a close relationship; (4) Sect. Carpinifolia , which has finely striate - reticulatoid exine sculpture, and Sect.

Key words: Pollen morphology