Background: Acute monocytic leukemia (AMoL) is an aggressive hematologic malignancy characterized by the uncontrolled proliferation of monocytes. Conventional therapies often fall short, necessitating the exploration of novel therapeutic approaches. Vanillin, a natural phenolic compound, has demonstrated various bioactivities, including antioxidant, anti-inflammatory, and anticancer effects. This study investigates the immunomodulatory and antioxidative properties of vanillin in the human acute monocytic leukemia cell line, THP-1. Methods: THP-1 cells were treated with varying concentrations of vanillin (50, 100, 200µM). The production of pro-inflammatory cytokines (TNF-α, IL-6) and anti-inflammatory cytokine (IL-10) was quantified using ELISA. Oxidative stress was assessed by measuring ROS levels, malondialdehyde (MDA) content, and the activities of antioxidant enzymes such as glutathione (GSH), catalase, and superoxide dismutase (SOD). Cellular and molecular characterization was performed using zeta potential analysis, atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FTIR). Results: Vanillin treatment resulted in a significant reduction in TNF-α and IL-6 levels, coupled with an increase in IL-10 production in THP-1 cells. These effects were dose-dependent, with higher concentrations of vanillin exerting more pronounced immunomodulatory effects. Vanillin also effectively reduced ROS levels and MDA content, while enhancing GSH levels, catalase activity, and SOD activity, indicating a robust antioxidative response. Physical and biochemical analyses revealed alterations in cell morphology and surface properties, suggesting that vanillin may induce apoptosis or other forms of cell death in leukemic cells. Conclusion: Vanillin exhibits significant immunomodulatory and antioxidative effects in THP-1 cells, highlighting its potential as a therapeutic agent for AMoL. By reducing pro-inflammatory cytokines, enhancing antioxidant defenses, and inducing cellular changes, vanillin may contribute to the suppression of leukemia cell proliferation and survival. These findings warrant further investigation into vanillin's mechanisms of action and its potential application in leukemia therapy.