Background: The etiology of systemic lupus erythematosus (SLE) is complex, and the disease is thus difficult to cure. In this regard, it has been established that SLE patients are characterized by differing levels of vitamin D-hydroxylation; however, the direct effects of vitamin D (VitD) in these patients remain unknown. Objective: Therefore, we investigated the effects and mechanisms of action of VitD in the context of SLE. Methods: The effects of VitD on MRL/LPR mice were studied by synthesizing glycogen synthase kinase-3β (GSK-3β)-interfering lentiviruses and transfecting with miR-126a-5p mimics. Changes in the body weight of mice were recorded for 6 weeks. Western blotting was performed to determine the levels of T-bet, GATA3, and GSK-3β protein expression, and qRT-PCR was performed to determine the levels of miR-126a-5p and GSK-3β mRNA expression. ELISA was performed to determine the levels of ANA, dsDNA, and snRNP/Sm in mice serum. method: The effect of VitD on MRL/LPR mice was studied by synthesizing GSK-3β-interfering lentivirus and transfecting miR-126a-5p mimics. Body weight changes were recorded for 6 weeks. Western blot was performed to detect T-bet, GATA3, and GSK-3β protein expression levels, and qRT-PCR was performed to detect miR-126a-5p and GSK-3β mRNA expression levels. ELISA was performed to detect ANA, dsDNA, snRNP/Sm levels in serum. Results: GSK-3β and miR-126a-5p were expressed at high and low levels, respectively, in MRL/LPR mice. VitD (30 ng/kg) was found to reduce the expression of GSK-3β and increase miR-126a-5p expression, which targets GSK-3β. T-bet and GATA3 were found to be positively regulated by miR-126a-5p and VitD and negatively regulated by GSK-3β. The body weight of mice was not altered by VitD. ANA, dsDNA, and snRNP/Sm were positively regulated by miR-126a-5p and VitD and negatively regulated by GSK-3β. The effects of GSK-3β were enhanced in response to the inhibition of miR-126a-5p expression. Conclusion: VitD upregulated miR-126a-5p to target GSK-3β expression, thereby alleviating the SLE in MRL/LPR mice. other: none