Natural polymeric materials extracted from plants are the new alternatives for synthetic polymers in wastewater treatment as they enhance the treatment’s efficiency besides of prominent characteristics, such as highly biodegradable, non-toxic, non-corrosive, less sludge voluminous and pH independent. The aim of this study is to evaluate the ability of Casia fistula seed gum (CFG) as a coagulant aid with PAC in the treatment of textile wastewater. Jartest experiments were carried out to identify the optimal parameters of coagulation-flocculation for removing color and COD in synthesis wastewater containing Methyl blue and RB21 dyes, including pH, settling time, PAC dose, the optimal CFG dosage in comparing with the cationic polymer. After that, actual textile wastewater was treated by using PAC, PAC plus cationic polymer, and PAC plus CFG for evaluating the role of CFG. CFG supplementation has assisted the process effects at nearly 98% color, 85% COD for RB21 and 90% color, 70% COD for MB at the best dose of CFG 0.15 mL and 0.1 mL, respectively. The optimized parameters for the coagulation of real textile wastewater using PAC were pH = 6 and dose = 0.6 mL can removal 66% of color. By adding CFG to PAC, the efficient of treatment was increased about 70% even at the lower dosage of PAC and CFG (0.5 mL for each reagent). The yield of combining PAC and polymer was a little bit lower than PAC and CFG, for instant 68% color was decreased at the same condition. These achievements demonstrated a workable substitute of natural products such as Cassis fistula seed gum for synthetic chemical products in coagulation-flocculation process.