Introduction/Aim HLA-B27/human β2m transgenic rats (B27-rats) develop an inflammatory disorder resembling spondyloarthritis (SpA) with dysregulated IL-10/IL-17 production by regulatory T cells (Treg). Treg plays a major role in controlling pathogenic inflammatory processes. Interleukin 2 (IL-2), a cytokine which promotes Treg cell survival and function, may thus have therapeutic efficacy in SpA. Here, we tested this hypothesis using a low dose of IL-2 treatment in B27-rat. Material and methods B27-rats aged 4 weeks (before disease onset) and nontransgenic (NTG) littermates were administered intraperitoneally recombinant human IL-2 (Sanofi®; 2,000IU/injection) or PBS, 3 days per week during 6 weeks. Assessment of treatment effect was performed, based on clinical (weight, diarrhea, arthritis), histological (proximal and distal colon, caecum, ileum and tarsal/ankle joint) scores, and frequency of Treg in the spleen and lymph nodes (LN). Results IL-2 administration had no effect on weight gain, either in B27- or NTG-rats. Over the 6 weeks of treatment, the clinical disease score worsened similarly in both IL-2-treated and control groups of B27-rats. The macroscopic and histological evaluation of gut and joints showed marked inflammation in B27-rats; however, no change related to IL-2 treatment was observed. In the B27-rats, the percentage of Treg was moderately increased after IL-2 treatment in the spleen, but neither in mesenteric nor peripheral LN in those rats. Conclusion Our data demonstrate that a low dose of IL-2 administered before disease onset was moderately effective for boosting Treg but failed to prevent SpA development in B27-rat.