Abstract: Adsorption of methyl orange dye (MO) on dried Pistia stratiotes in simulated wastewater was investigated in an experiment, to explore effects of factors, such as adsorption duration, initial pH of the solution, dosage of dried Pistia stratiotes and initial MO concentration on the adsorption. Results show that when the wastewater was 5.5 in initial pH, and 25mg•L^-1 in initial MO concentration, by adding 12.5 g•L^-1 of dried Pistia stratiotes with 0.250-0.425 mm in particle size, was then the solution was shaken on a vibrator at 120 r•min^-1 for 90 min under the room temperature (25 ºC), up to 72.1% of the MO in the wastewater could be removed. It was found that lower pH was conducive to MO adsorption; within a certain range, adsorption rate increased with dosage of the adsorbent dosage and initial concentration of MO in the solution. The adsorption data showed that the process of the adsorption fitted the Freundlich adsorption isothermal equation quite well and dynamic behavior of the adsorption did the Lagergren pseudo-second-order kinetics equation well. With rising temperature, MO equilibrium adsorption capacity decreased. Analysis of the Pistia stratiotes and its extractant shows that chromium,nickel,copper,arsnic,cadmium and lead contents therein were far below the limit set in GB5085.3-2007 (Identification Standard for Hazardous Wastes-Identification for Extraction Toxicity). Therefore, dried Pistia stratiotes can be used as a new type of adsorbent in dyeing wastewater treatment without risk of secondary pollution.