Abstract: Artificial salt soil and five nature salinized soils are used to investigate the effect of arbuscular mycorrhizal (AM )fungi on the saline tolerance of cotton．The results show that the inoculation with AM fungi increases the biomass of cotton plant under both artificial and nature salinized soils significantly．The effects of AM fungi on cotton growth are also promoted with the increa se of salt 1evels．This may indicate that the mycorrhizal-plant association is bcneficia1 for plant growth in salinity environment．Phosphorus concentrations in non-mycorrhizal plant show a up trend with saline level increasing and mycorrhizal plants have higher phosphorus concentration at all salt levels than that of non-mycorrhizal plants．This indicates that cotton plant needs more phosphorus to maintain metabolism and growth under salt stress．