With the increasing global concern about environmental issues, researchers are increasingly interested in the use of natural biopolymers to replace inorganic coagulants in order to reduce the use of inorganic coagulants. The removal of diethylhexyl phthalate (DEHP) from secondary effluent by guar gum was investigated and compared with that of alum. Guar gum effectively removed approximately 92.11% of turbidity, 71.47% of total phosphorus, and 54.84% of chemical oxygen demand at a dosage of 3 mg L-1. Further, evaluation and optimization of reaction conditions of coagulation-flocculation process in wastewater treatment by Box-Behnken design of Response Surface Methodology (RSM). The results indicated that a guar gum dosage of 3 mg L-1 at pH=7 resulted in the removal of 78.93% of DEHP. SEM showed that guar gum produces flocs with many voids in them compared with alum. This illustrates the greater availability of guar gum in catching and removing particles in suspension and DEHP compared with alum. FTIR indicated that organic matter in the effluent had chemically attached to the coagulants, leading to the removal of the organic matter. Given its nontoxicity and biodegradability, guar gum demonstrates promising potential as a coagulant in wastewater treatment.