Abstract: The growth and glyphosate tolerance of alligator weed (Alternanthera philoxeroides) under high level of manganese(Mn) condition were studied.The results showed that when treated with 8-128 mg/kg Mn in the soil for 20 days,the branch numbers of alligator weed were significantly increased by 22.57%-48.31% compared to that of the control (4.43 per plant),the length of the longest stems was significantly increased by 16.60％-19.87% compared to that of the control (23.85 cm),the total rhizomes number were significantly increased by 29.87％-47.40% compared to that of the control (1.54 per plant),and the dry weight of the alligator weed were significantly increased by 22.45%-27.00% compared to that of the control (0.23 g).The areas of the leaves were also larger than that of the control in 32-128 mg/kg Mn treatment.21 days after the application of glyphosate in the dosage of 68,102 and 136 g ae/ha,the reduction of fresh weight of alligator weed declined by 27.39%,24.57% and 30.06%,respectively,in Mn 128 mg/kg treatment.The results indicated that the growth and propagation of alligator weed were stimulated when the Mn content in soil was increased,and this might be one of the major reasons leading to the spreading of the weed in acidic soil environment.Alligator weed showed remarkably tolerance to glyphosate under high Mn condition in the soil,implying it might be difficult to control the weed in the future.