Conclusions O. basilicum L. has been found to be a highly effective coagu-lant agent for the treatment of textile wastewater. Only 1.6 mg/Lof the coagulant has the ability to decolorize congo red dye solu-tion with a concentration of 250 mg/L. The natural coagulant keepsits coagulation power over the pH range of 6.0–8.5. Up to 68.5%dye removal and 61.6% COD reduction was achieved at 50 mg/L dyeconcentration, pH 6.5 and 1.6 mg/L coagulant dose. The O. basilicummucilage can be used in treating real textile wastewater either as a sole coagulant or in combination with alum as a coagulant aidwith high efficiency. The obtained results indicate that O. basilicumhas a promising potential to be used as an inexpensive bio-basedcoagulant for the treatment of industrial wastewaters.