Abstract: Objective To explore the relationships between serum 25-hydroxyvitamin D₃ level and T-lymphocyte subsets as well as interferon-α(IFN-α)levels in patients with systemic lupus erythematosus. Methods Totally 44 patients with systemic lupus erythematosus were selected as study group, and 44 healthy people with physical examination in the same period were selected as control group. The levels of serum hydroxyvitamin D₃ and IFN-α were detected by chemiluminescence microparticle immunoassay, and the expression of T lymphocyte subsets was detected by flow cytometry. The relationships between serum 25-hydroxyvitamin D₃ level and T-lymphocyte subsets as well as IFN-α levels were analyzed. Results The levels of serum 25-hydroxyvitamin D₃ and T lymphocyte subsets in the study group were significantly lower, and IFN-α level was significantly higher than that in the control group(P<0.05). There were significant relationships between serum 25-hydroxyvitamin D₃ level and T-lymphocyte subsets as well as IFN-α levels in patients with systemic lupus erythematosus(P<0.05 or P<0.01). Conclusion The level of serum hydroxyvitamin D₃ is closely correlated with expression of T-lymphocyte subsets and IFN-α level in patients with systemic lupus erythematosus.