Narrow-leaved cattails were studied in synthetic reactive dye wastewater (SRDW) under caustic conditions. The effects of the toxic dye were expressed in terms of relative plant growth rate and the appearance of symptoms such as necrosis, and chronic or acute wilting. The dye toxicity was 25.33 mg l⁻¹ which was close to approximate the concentration of dye residue from the textile effluent in the public stream. The system pH and % color removal were decreased, indicating that narrow-leaved cattail can treat wastewater. The average system pH decreased from 9 to 7. The maximum color removal was approximately 60% when cultured under soil conditions. The SEM image of narrow-leaved cattail root after treatment with SRDW indicated that the root cortex was damaged and the crystalline sodium salts deposited in the root cells which caused evaporation and transpiration decreased in SRDW. The salinity under caustic conditions also affects the growth of the plants. The maximum sodium removal was approximately 44% and was found in the SRDW under soil conditions within 14 days. A small amount of sodium could enhance the relative growth rate. However, the sodium removal of the plants was limited after the third week of treatment. It should be noted that narrow-leaved cattails are known to avoid the textile dye and salt stress conditions during SRDW treatment through special mechanisms such as salt accumulation in the roots or shedding of older leaves. In addition, elements such as silicon, calcium and iron in plants might help the plant to detoxify by forming complexes with dye molecules.