An investigation was conducted of the alt iplano grassland,which was the important agricultural and animal husbandry base in Tibet.Soil samples with roots,2 kg each,were collected from the rooting-zone of 22 dominant plants at a depth of 2~30 cm and each sample had three replicates.Then the soil samples were ai-rdried,sieved through a 2 mm sieve and stored at 4℃.The root samples were rinsed with tap water,soaked in 10% (w/v) KOH(30 min,90℃),acidified in lactic acid(10 min),and stained with 0.5% trypan-blue.Thirty 0.5 to 1 cm root fragments were examined per sample for their arbuscular mycorrhizal status under a compound microscope(×200).A hundred grams of soil were taken from each sample and wetsieved.Then AMF spores were counted on a grid pattern dish under a binocular stereomicroscope.Spores of AM fungi isolated from the field soil and trap cultures were mounted on glass slides in polyvinyl-lacto-glycerol(PVLG).Then spores examined microscopically and identified according to current taxonomic criteria(Schenck and Prz,1990) and internet information from INVAM(http://invam.caf.wvu.edu).The results show that the invest igation of resources and ecological distribution of arbuscular mycorrhizal fungi(AMF) were contributive to the study on diversity of AM fungi in the alt iplano grassland in Tibet.Five genera of AM fungi were collected and identified in the sampled soils.In terms of spore density,isolation frequency,relative abundance and importance value,they were in the order of Glomus>Acaulospora>Gigaspora>Scutellospora>Entrophospora.Glomus,but they all were of prominent genus in the investigation area and Acaulospora,Gigaspora and Scutellospora were of common genus while Entrophospora was rarely found.The appearance and distribution of AMF are related to regional difference,soil factors and plant hosts.Among the five genera,Gigaspora,Glomus and Acaulospora were distributed widely in the target areas,while Scutellospora and Entrophospora were only found in altiplano grassland.The diversity character was similar in most areas,only Acaulospora appeared more frequently in frigid meadow.Under different meadow types and soil texture,the diversity of AM fungi was in the trend of frigid meadow>upland brushy grassland>meadow,and loam>sandy loam and heavy sandy soil> light sandy soil.AM fungi were the commonest in the soil with pH in the level of 6.0~6.7,olsen P in 5.3~13.8 mg kg^-1 and organic matter in 35.7~54.6 g kg^-1.AM fungi colonized well in the plants of Carex praecpara,Kobresia humilis and Cyperus compressus,but not in Fagopyrum esculentum.Tamarix chinensis and Salsola nepalensis,commonly recognized as good host,were not colonized,either.It was also found soil pH was positively correlative to spore density,but not to colonization.