OBJECTIVE： To study the effects of Arbuscular mycorrhizal （AM） fungi on yield and its active ingredients contents of Saussurea costus in artificial cultivation. METHODS： Through the pot method at room temperature， not inoculated AM fungi group was regarded as CK group， inoculated AMykor mycorrhiza group as AM group， 5 repeated in each group， one pot in each repeated， there were 5 pots in all， 3 strains of S. costus in each pot. Literature establishment method was used to calculate the mycorrhizal colonization rate and colonization intensity. Weighing method was adopted to determine the yield and HPLC was conducted to determine the content of costunolide and dehydrocostuslactone. RESULTS： Colonization rates of AM group and CK group were （86.22±3.28）％， 0 （P＜0.05）； colonization intensities were （52.12±2.14）％， 0 （P＜0.05）. There were statistical significances in weighing rate of root， contents of costunolide， dehydrocostuslactone and total lactones in 2 groups （P＜0.05）. Compared with CK group， the yield increase in AM group （50.96±2.12）％， contents of costunolide， dehydrocostus lactone and total lactones increased 65.55％， 97.42％， 85.42％， respectively. And there was a certain change on the structure ratio of lactones. CONCLUSIONS： Inoculating exogenous AM fungi can significantly improve the root quality of S. costus.