Bentonite was modified by intercalation of amino acids into its interlayer space. Different amounts of L-glutamic acid were added to bentonite and its effect was investigated on the reduction of landfill leachate contamination. In the best result, the effect of pH adjustment on the structure and performance of the modified clay was studied. The composite was characterized by various techniques such as FTIR, SEM, XRD, TGA, and BET. Batch experiments were performed to evaluate the factors influencing leachate chemical oxygen demand (COD) and turbidity removal efficiency. The effect of surfactant loading amount, contact time, pH, and adsorbent dosage was evaluated. Under optimum conditions, the maximum COD and turbidity removal rates for row clay were 40.1% and 63.8%, respectively, but they were 65.7% and 92.1% for amino acid-modified clay under pH adjustment conditions, respectively. Also, the results showed that the adsorbent produced in pH adjustment conditions had higher efficiency for leachate treatment than the synthesized adsorbent under non-pH adjustment conditions. Under optimum conditions, the percentage of COD and turbidity removal for modified clay under pH adjustment was 65.7% and 92.1%, respectively, while they were 61.3% and 89.9% for non-pH adjustment, respectively.