Background: Abortion was defined as loss at a gestational age less than 28 weeks. Vitamin D is reported to be associated with reproductive functions, whereas its casual effects on abortion remains unclear. In this study, a two-sample Mendelian randomization (MR) analysis was performed to systematically assess the causal relationships between serum 25 hydroxyvitamin D concentration and the risk of abortion. Results: GWAS summary data of vitamin D was used as exposure, and data of missed abortion and spontaneous abortion was considered as outcome. A retrospective study was also conducted to verify the associations identified from MR study. MR estimates showed that a higher Vitamin D level was associated with decreased risk of both missed abortion and spontaneous abortion. However, the P value was not significant. We then conducted a retrospective study, and observed the consistent result of Vitamin D’s protective role to abortion. The value was very close to statistical significance (P=0.0527). Conclusions: This study reports the potential protective role of serum 25 hydroxyvitamin D concentration to abortion, that is, higher Vitamin D levels can decrease risk of abortion. Further larger retrospective study is needed to confirm this association.