Objective: To detect the mRNA levels of genes of BMP/Samd signaling pathway in peripheral blood mononuclear cells of patients with systemic lupus erythematosus (SLE) and to determine their correlations with the ratio of OPG/RANKL, thus to further investigate the effect of BMP/Smad pathway on the bone metabolism of SLE patients. Methods: The mRNA levels of RANKL, OPG, BMP-2 and Smad1/5/8 gene in peripheral peripheral blood mononuclear cells from 26 SLE patients and 20 normal controls were detected by rea1-timePCR (RT-PCR), and the protein level of OPG and RANKL were measured by ELISA. The correlation analysis between these genes of BMP/Smad signaling and the ratio of OPG/RANKL or some indexes of disease activity were studied. Results: The mRNA levels of OPG decreased in SLE patients compared with normal controls (0.002 5 ± 0.000 7 vs. 0.017 6 ± 0.006 7, P < 0.05), and RANKL levels had no differences between the two groups (0.003 3 ± 0.001 0 vs. 0.002 4 ± 0.000 9, P > 0.05), which led to a decreased ratio of OPG/RANKL (0.229 6 ± 0.071 2 vs. 0.609 5 ± 0.165 1, P < 0.01). Both the mRNA levels of Smad1 and Smad8 were significantly decreased in SLE patients than those in controls (0.003 1 ± 0.000 4 vs. 0.006 6 ± 0.000 7; 0.003 3 ± 0.000 5 vs. 0.005 6 ± 0.000 6,P <0.01), and also the level of Smad5 was decreased (0.001 7 ± 0.000 3 vs. 0.004 2 ± 0.000 4, P < 0.05). There were no differences on the BMP-2 gene expression between the two groups (0.006 9 ± 0.002 0 vs. 0.010 5 ± 0.002 1,P > 0.05). Serum protein levels of RANKL were higher in SLE patients than those in controls (P < 0.01), while OPG levels had no differences between the two groups, which led to an decreased ratio of OPG/RANKL (P = 0.006) in SLE patients. Analysis showed that positive correlation between mRNA level of Smad8, ratio of OPG/RANKL and ESR levels of SLE patients (P < 0.05). Moreover, mRNA levels of Smad8 and OPG were found positively related (P < 0.01), while that of Smad1 and RANKL were negatively related (P < 0.01). Conclusion: The gene expressions of BMP/Smads signaling pathway were abnormal in SLE patients, which may be involved in the mechanism of unbalanced bone metabolism of patients.