In this study, it was intended to explore the causal association between mean platelet volume (MPV) and risk of deep vein thrombosis (DVT) using a two-sample Mendelian randomization (MR) analysis and a retrospective study.This study applied two-sample MR analysis to estimate the causal association between MPV and risk of DVT. Twenty-one single nucleotide polymorphisms (SNPs) were selected as genetic variants from two independent consortiums cohorts (p-value <5×10-8, linkage disequilibrium r2<0.1). Inverse variance weighted (IVW), MR-egger method and weighted median were performed. A retrospective study was also conducted to verify the associations identified from the MR study.The MR analysis demonstrated that genetically predicted higher MPV was associated with significantly lower risk of DVT (OR 0.982, 95% CI = 0.967-0.998, P = 0.023), with the consistent result in weighted median and MR-Egger. There was no directional horizontal pleiotropy in the method of MR-Egger regression (intercept=2.9e-04, P = 0.194). There was no single SNP was found to strongly drive the combined causal effect in the leave-one-out sensitivity analysis. Additionally, the similar result was observed in the retrospective study.This study suggested that MPV was negatively associated with the risk of DVT. More basic researches are needed in the future to explore its specific mechanism.© 2023 Li and Liang.