Background: Protease inhibitors have been isolated from plants and present several biological activities, including immunomodulatory action. Objective: This work aimed to evaluate a Moringa oleifera flower trypsin inhibitor (MoFTI) for acute toxicity in mice, hemolytic activity on mice erythrocytes and immunomodulatory effects on mice splenocytes. Methods: The acute toxicity was evaluated using Swiss female mice that received a single dose of the vehicle control or MoFTI (300 mg/kg, i.p.). Behavioral alterations were observed 15–240 min after administration, and survival, weight gain, and water and food consumption were analyzed daily. Organ weights and hematological parameters were analyzed after 14 days. Hemolytic activity of MoFTI was tested using Swiss female mice erythrocytes. Splenocytes obtained from BALB/c mice were cultured in the absence or presence of MoFTI for the evaluation of cell viability and proliferation. Mitochondrial membrane potential (Δψm) and reactive oxygen species (ROS) levels were also determined. Furthermore, the culture supernatants were analyzed for the presence of cytokines and nitric oxide (NO). Results: MoFTI did not cause death or any adverse effects on the mice except for abdominal contortions at 15–30 min after administration. MoFTI did not exhibit a significant hemolytic effect. In addition, MoFTI did not induce apoptosis or necrosis in splenocytes and had no effect on cell proliferation. Increases in cytosolic and mitochondrial ROS release, as well as Δψm reduction, were observed in MoFTI-treated cells. MoFTI was observed to induce TNF-α, IFN-γ, IL-6, IL-10, and NO release. Conclusion: These results contribute to the ongoing evaluation of the antitumor potential of MoFTI and its effects on other immunological targets.