Objective To investigate the correlation between untreated premenopausal women with sys-temic lupus erythematosus(SLE)and 25 hydroxyvitamin D[25(OH)D]levels.Methods A total of 80 newly diagnosed premenopausal female SLE patients admitted to our hospital from July 2020 to June 2023 were se-lected as the SLE group,and 80 healthy premenopausal women were selected as the control group during the same period.Chemiluminescence method was used to detect the level of 25(OH)D,ELISA to detect autoanti-bodies in SLE patients,and the proportion of SLE patients with 25(OH)D deficiency or insufficiency was ana-lyzed.Pearson correlation analysis was used to investigate the correlation between 25(OH)D and 24-hour uri-nary protein quantification,complement 3(C3),complement 4(C4),systemic lupus erythematosus activity(SLEDAI)score,and specific lupus autoantibody titers in SLE patients.Multiple logistic regression was used to analysis the risk factors for developing SLE in premenopausal women.The receiver operating characteristic(ROC)curve and area under the curve(AUC)were used to analyze the value of various indicators in predic-ting the occurrence of SLE in premenopausal women.Results The serum 25(OH)D level in the SLE patient group was lower than that in the control group(P＜0.05).According to the diagnostic criteria for vitamin D deficiency and insufficiency,the proportion of patients with vitamin D deficiency in the SLE group was 22.50％(18/80),and the proportion of patients with vitamin D deficiency was 63.75％(51/80).The serum levels of C3 and C4 in SLE patients were lower than those in the control group(P＜0.05).The levels of anti-double stranded DNA(dsDNA)antibody and anti-cardiolipin IgG(CL IgG)antibody were higher than those in the control group(P＜0.05).Pearson correlation analysis showed that serum 25(OH)D levels in SLE pa-tients were negatively correlated with anti-CL IgG antibody,anti-dsDNA antibody,24-hour urine protein quan-tification,and SLEDAI scores(r=-0.339,-0.294,-0.328,-0.392,P＜0.05),and positively correlated with complement C3 and C4 levels(r=0.241,0.178,P＜0.05).Multivariate logistic regression analysis showed that 25(OH)D,anti-dsDNA antibody,anti-CL IgG antibody,C3,C4,24-hour urinary protein quantifi-cation level,and SLEDAI score were independent influencing factors for the occurrence of SLE in premenopa-usal women(OR=1.125,0.413,0.203,99.791,33.162,0.045,0.096,P＜0.05).The AUC of each indicator predicting the occurrence of SLE in premenopausal women were 0.911,0.800,0.768,0.978,0.893,and 0.893,re-spectively.Conclusion 25(OH)D plays an important role in the onset and development of SLE and can be used as a predictive indicator of disease activity.It is recommended to screen for 25(OH)D in newly diagnosed SLE patients and treat patients with deficiency or insufficiency.