Abstract: The aim of this paper is to investigate the effects of different forms of exogenous organic matters on the assimilation of nitrogen and production of arginine (Arg) by arbuscular mycorrhizal (AM) fungus. AM fungi (Glomus intraradices) were inoculated to the host plant (Sorghum bicolor L. Moench) and grown in the three-compartment pot culture system, 4mmol/L NH4NO3 was added into the mycelium compartment, and different forms of carbons were added into the root compartment. The Arg and total nitrogen contents were determined and analysed in extraradical mycelium (ERM), mycorrhizal roots and shoots separately. The results show that the contents of Arg in ERM and mycorrhizal roots are significantly higher than that those in shoots. The dry weight of ERM and root infection rate are increased under the adding of different forms of organic matters, while the Arg contents in ERM, mycorrhizal roots and shoots are reduced under the adding of glucose. The production of Arg is not significantly affected under the adding of sucrose and glycerol, while the Arg content in ERM is significantly increased under the adding of external Arg and glutamine (Gln). The different forms of carbons have no significant effects on total nitrogen contents in mycorrhizal roots and shoots. Therefore, the carbon for Arg biosynthesis is mostly derived from the carbohydrates of the host plants supply, however the exogenous carbon could promote the growth of AM fungus.