Background: Inflammatory bowel disease (IBD) comprises primarily the two disorders - ulcerative colitis and Crohn's disease - that involve deregulated T cell responses. The ever-increasing incidence rate of Crohn's disease and ulcerative colitis during recent decades, combined with the limited efficacy and potential adverse effects of current treatments, explain the real need for seeking more specific and selective methods for treating these diseases. Aim: To investigate the ability of interleukin 2 (IL2)-caspase 3 chimeric protein, designed to target activated T lymphocytes that express the high-affinity IL2 receptor, to ameliorate the clinical symptoms of acute murine experimental colitis, using a mouse model of dextran sodium sulfate (DSS)-induced colitis. Methods: Mice with DSS-induced colitis were treated with IL2-caspase 3 for 7 days and disease severity was assessed in parallel to control, non-treated mice, receiving only daily injections of phosphate-buffered saline. IL2-caspase 3 was tested both for its ability to prevent the development of colitis, and for its therapeutic potential to cure on-going, active acute disease. In addition, colon tissue samples were used for myeloperoxidase assays and RNA isolation followed by polymerase chain reaction to determine mRNA expression levels of specific genes. Results: Treatment with IL2-caspase 3 dose-dependently ameliorated the disease activity index (DAI) of mice colitis. We achieved up to 78% improvement in DAI with intravenous injections of 15 mg/mouse/day. Furthermore, IL2-caspase 3 decreased neutrophil and macrophage infiltration to the inflamed tissue by up to 57%. IL2-caspase 3 was proven as a therapeutic reagent in another model, where treatment begins only after disease onset. Here we demonstrated a 70% decrease in DAI when compared to non-treated sick mice. A reduction in mRNA expression levels of both IL1β and tumour necrosis factor α was found in lysates of total colon tissue of treated mice, as compared to sick, untreated mice. We also found that expression levels of Bcl2 were significantly decreased after treatment, while Bax was upregulated in comparison to non-treated mice. Moreover, the Bcl2/Bax ratio, which is elevated in both experimental colitis and in human Crohn's disease, decreased dramatically after treatment. Conclusions: IL2-caspase 3 chimeric protein may provide a novel approach to the therapy of human IBD, and a possible suggested treatment for other pathological conditions that involve uncontrolled expansion of activated T cells.