In the present study, facile and cost-effective modification methods, including alkali treatment and acid treatment, were evaluated to improve the adsorption capacity of NaY zeolite for diclofenac sodium (DFS) elimination from the aqueous solution. The performance of unmodified NaY, sodium hydroxide treated NaY (SHT-Y), hydrochloric acid treated NaY (HAT-Y), and sulfuric acid treated NaY (SAT-Y) was compared, followed by optimization of sulfuric acid concentration since sulfuric acid was recognized as the preferred modifying agent. The modified NaY with a concentration of 0.1 M of sulfuric acid exhibited the highest adsorption capacity. Analyses of FE-SEM, EDS, FTIR, BET, and XRD were used to determine the characteristics of NaY and treated zeolites. All treatments changed the Si/Al ratio of NaY. Silanol and bridging hydroxyl functional groups were detected in all zeolitic samples. Acidic modifications enhanced the specific surface area of NaY more than the alkali treatment. The influence of the major factors on the DFS adsorption, including adsorbent dosage, contact time, pH of the solution, and initial concentration of DFS was investigated and optimized in detail. The maximum adsorption capacity was obtained at pH 11 at the equilibrium time of 180 min. The hydrogen bond formation and cation-π interaction were recognized as DFS adsorption mechanisms. From the results of kinetic studies, the Elovich model has better agreement with experimental data, suggesting that the adsorbent surface is energetically heterogeneous and chemisorption leads the DFS uptake onto the adsorbent, indicative of hydrogen bond formation. In accordance with the equilibrium modeling results, the Sips isotherm better expresses the DFS adsorption mechanism onto the surface of the modified zeolite. According to the Langmuir isotherm model, the maximum adsorption capacity obtained for 0.2 g/L of treated zeolite was 117.77 mg/g. Eventually, sulfuric acid treatment was found as an effective and facile method for enhancing zeolite performance in DFS removal from aqueous solution.