Abstract: In order to investigate the influences of carbendazim on AM fungus infected tobacco seedlings and mycorrhizal effect,the experiment of AM fungus inoculating and carbendazim applying was conducted in a seedling floating system.The results showed that AM fungus inoculation generally promoted the growth of tobacco seedlings,while mycorrhizal effects varied with fungal strains.When applied carbendazim was at a low concentration(dilution 500),the tobacco seedlings' biomass,content and absorption of phosphorus,chlorophyll content and chitinase activities increased to different extents by the inoculation of Glomus intraradices Smith(BEG-141) or Glomus intraradices Schenck(BEG-193);while when applied carbendazim was at a high contentration(dilution ≤ 500),the infected ratio to AM fungus and mycorrhizal effect decreased and the growth of tobacco seedlings was inhibited.The two fungal strains differed in the susceptibility to carbendazim,the growth of tobacco seedlings with BEG-193 was not susceptible,while the growth of tobacco seedlings with BEG-141was inhibited by high concentration carbendazim.Therefore,it is suggested that carbendazim should be applied at a low concentration(dilution 500) to ensure normal seedling growth and the improvement of nutrition conditons and stress resistance offered by AM fungus.