In order to investigate the physiological effects of lanthanum nitrate and orchid mycorrhizal(OM) fungi on Dendrobium officinale,we investigated the effects of inoculation with OM fungi under different lanthanum nitrate application levels (0,1.0,3.0,5.0 and 7.0 mg·L^-1) on the biomass of D.officinale seedling and synthesis of polysaccharides and proteins using a pot experiment.The chlorophyll content,malondialdehyde (MDA) content and the activities of SOD,CAT and POD in cells were analyzed.The results were as follows:(1)Appropriate concentration of lanthanum nitrate was beneficial to the development of mycorrhiza and promoted the biomass of D.officinale seedling.(2)D.officinale inoculated with OM fungi and applied with lanthanum nitrate 5.0 mg·L^-1 had the largest mass of roots,mass of shoots and biomass of D.officinale seedling which were of 4.26,4.98 and 4.87-fold,respectively,compared to control.The infection rate of OM fungi to the roots of D.officinale seedling reached 92.8%.The contents of chlorophyll increased,whereas the content of MDA decreased in cells.(3)The contents of polysaccharides and proteins increased in cells.SOD,CAT and POD activities were found to increase significantly in cells too on the same conditions.Therefore,the development of D.officinale mycorrhiza,the physiological activity and adaptability of plants,the biomass of D.officinale seedling and accumulation of polysaccharides could be improved by inoculation with OM fungi and application with appropriate concentration of lanthanum nitrate (5.0 mg·L^-1).It indicated that the medicinal qualities of D.officinale could be promoted too.