Objective:To investigate the expression level of miR-518d in the placenta and maternal serum of gestational diabetes mellitus and normal pregnant women. Methods:The expression of miR-518d in placenta and serum was measured by Taqman RT-PCR in 20 women with GDM and 20 women with normal term pregnancy. Results:Expression of miR-518d in placenta was significantly up-regulated in GDM group(4.35 ± 0.88)compared to control group(1.04 ± 0.73)(P < 0.01). Expression of miR-518d in serum was also up-regulated in GDM group(2.43 ± 1.07)compared to control group(0.96 ± 0.88)(P < 0.05). We also showed that PPARa was a direct target of miR-518d with a specific binding site at the seed sequence. And expression of miR-518d in the placenta was significantly positive correlated with the expression of serum E2(R2=0.759,r = 0.871). Conclusion:miR-518d is related with the mechanism of GDM and we suggest that upregulation of miR-518d may be associated with the pathogenesis of GDM via an effect on the regulation of PPARα expression.