Abstract: To determine the effects of symbiotic fungi on the growth and physiological characteristics of endangered Dendrobium catenatum(Orchidaceae),asepsis seedlings of this species were inoculated with fungi strains C20,C22,C35,and C42 in the laboratory.After 60 days co-culture,the average increase rate of fresh weight,nutrient elements,chlorophyll and endo-genous hormone were studied using the seedling without fungi inoculation as the control.Our results showed that(1)the fungi strains could be re-isolated from the roots of the experimental seedlings,which indicated that the fungi were successfully inoculated into the seedlings;(2)The average increase rate of fresh weight,the content of chlorophyll a and b and the content of N,P and K in inoculated seedlings were higher than that in the control;(3)GA₃ and IAA concentration in inoculated seedlings were higher,but ABA concentration was lower than in the control.Notably,the average increase rate of fresh weight and content of chlorophyll a in seedlings inoculated with C42 were significantly higher than that in the control(p<0.01).Seedlings inoculated with C22 and C35 also showed significantly higher average increase rate of fresh weight and content of chlorophyll a as compared with the control(p<0.05).The content of K in seedlings inoculated with C20 and C42 were significantly higher than that in the control,and IAA concentration in seedlings inoculated with C20,C35 and C42 were also significantly increased.In all of the inoculated seedlings,the contents of N and GA₃ were significantly higher,but the ABA concentration was significantly lower than that in the control.Therefore,these four fungi could be applied in the cultivation and reproduction of Dendrobium catenatum and other orchids.