Abstract: The relationship between host planting density and sporulation of arbuscular mycorrhizal(AM) fungi was investigated.Acaulospora longula were inoculated into bahia grass pots with 1,5 or 10 plants.After 4 months growth,the AM colonization were much higher in pots with 1 plant than that in pots with 5 or 10 plants,but no difference in the vesicle percentage and arbuscle percentage was observed.Although the shoot biomass didn't vary between 3 planting densities,the root biomass and spore density decreased with the increasing of planting density.Correlation analysis revealed a close relationship between root biomass and spore density.The result suggests that high planting density probably reduces the carbohydrate partitioned to the roots,and further retards the sporulation.