Arbuscular mycorrhizal fungi (AMF) form mutualistic symbiotic associations with the roots of approximately 80% of terrestrial plant species. AMF are an important component of ecosystems, and the diversity of the AMF could largely influence plant biodiversity, ecosystem variability and productivity. Dujiangyan, located in the upper reaches of the Yangtze River in subtropical region of Sichuan province in southwest China with a complex geographic environment, is rich in biodiversity. To investigate the effect of environmental factors, particularly altitude-related factors and disturbance, on AMF diversity, a survey of the diversity and ecology of AMF was carried out in Dujiangyan in August 2001.Three sampling sites were selected in the present study, which represented different habitats: Banruosi, the natural evergreen broadleaved forest; Longchi, the natural subalpine forest; and Mantoushan, a seriously disturbed site, in which all woody plants were cut about 20 years ago and annuals were dominant. A total of 85 common plant species were chosen, of which 51 plant species were sampled from Banruosi, 19 from Mantoushan, and 19 from Longchi (some species were simultaneously collected from the different sites). Of the 85 plants, 51 species belong to the angiosperms, 31 belong to the pteridophytes, and 3 belong to the Gymnosperms. Roots collected from each plant were cleaned and preserved in 50% ethanol. The percentage of root length colonized by AMF was quantified according to the magnified line-intersect method. Concurrently with root sample collection, a total of 58 rhizosphere soil samples were collected, of which 30, 16, and 12 were sampled from Banruosi, Longchi and Mantoushan, respectively. The soil samples were placed in sterilized cotton-cloth bags, labeled, and air-dried in shade for one week. The soils were cleaned, ground, sieved with a 2 mm sieve, stored at 4 ℃, and processed within three months. AMF spores were isolated from 100 g air-dried soil from each sample using the wet-sieving and decanting method.Seventy-eight (91.8%) out of 85 plant species examined were colonized by AMF; this group included 49 (96.1%) out of 51 angiosperms, 26 (83.9%) out of 31 pteridophytes, and 3 (100%) out of 3 gymnosperms. In total, 47 taxa of AMF belonging to 5 genera were isolated from the 58 soil samples, of which 35, 31, and 9 taxa were found in Banruosi, Mantoushan and Longchi, respectively. Thirty-two (68%) taxa were identified at species level, and the other 15 (32%) taxa were identified at genus level. In the 47 taxa, 35 belonged to the genus Glomus, 7 to Acaulospora, 1 to Archaeospora, 2 to Entrophospora, and 2 to Gigaspora. Acaulospora and Glomus both were the dominant genera in the three sites. Acaulospora laevis was the dominant species in Longchi, and Glomus versiforme was the dominant species in Banruosi and Mantoushan. There were no significant differences in spore density or species richness between Banruosi and Mantoushan, while they were significantly higher in Banruosi and Mantoushan than in Longchi. The highest AMF diversity index occurred in Banruosi (2.66), followed by Mantoushan (1.96) and Longchi (1.71). There was no significant correlation between the spore density and the percentage of root length colonized by AMF based on the analysis of linear regression (R2=0.024 8). It could be concluded that the species composition of AMF was greatly influenced by altitude-related factors, but lightly influenced by deforestation.