In this study, Ocimum basilicum L. (basil) has been evaluated as an active natural coagulant for the removal of dye from a model textile wastewater containing congo red. The effect of three parameters including pH, coagulant dose and dye concentration on the color removal and COD reduction were analyzed. A cubic equation could model the color removal process with a R2 of 0.89. The dye concentration was found to be the most significant parameter affecting the color removal. A high color (68.5%) and COD (61.6%) removal efficiency was obtained by using a low amount of the coagulant, 1.6 mg/L. The mucilage of O. basilicum was also found to be highly effective in treating real textile wastewater as a sole coagulant and in combination with alum.