Abstract: Influence of ammonium sulphate on translocation and phytotoxicity of glyphosate in alligator weed Alternanthera philoxeroides (Mart.) Griseb. was conducted. The results indicated that the inhibition of glyphosate to rhizome regrowth was increased by 12.2 percent, with the treatment of glyphosate (300 mg/L) and ammonium sulphate(1.20 g/L) mixture, comparing with treatment of glyphosate alone. The concentration of 14C-glyphosate in rhizomes and roots were 1.39 and 1.86 times more than that in control, respectively, which was treated with ammonium sulphate before 14C-glyphosate was applied. The results also showed that glyphosate phytotoxicity was reduced when water hardness was more than 342.0 mg/L, and it was restored by adding ammonium sulphate in concentration of 12.0 g/L.