Objective:To explore the molecular pathogenesis of a family with hereditary factor Ⅴ (FⅤ) deficiency.Methods:All the exons, flanking sequences, 5′ and 3′ untranslated regions of the F5 of the proband, and the corresponding mutation sites of the family members were analyzed via direct DNA sequencing. The CAT measurement was used to detect the amount of thrombin produced. The ClustalX software was used to analyze the conservation of mutation sites. The online bioinformatics software, Mutation Taster, PolyPhen-2, PROVEAN, LRT, and SIFT were applied to predict the effects of mutation sites on protein function. The Swiss-PdbViewer software was used to analyze the changes in the protein model and intermolecular force before and after amino acid variation.Results:The proband had a heterozygous missense mutation c.1258G>T (p.Gly392Cys) in exon 8 of the F5, and a heterozygous deletion mutation c.4797delG (p.Glu1572Lys fsX19) in exon 14, which results in a frameshift and produces a truncated protein. Her grandfather and father had p.Gly392Cys heterozygous variation, whereas her maternal grandmother, mother, little aunt, and cousin all had p.Glu1572LysfsX19 heterozygous variation. The ratio of proband's thrombin generation delay to peak time was significantly increased. Conservation analysis results showed that p.Gly392 was located in a conserved region among the 10 homologous species. Five online bioinformatics software predicted that p.Gly392Cys was pathogenic, and Mutation Taster also predicted p.Glu1572Lys fsX19 as a pathogenic variant. Protein model analysis showed that the replacement of Gly392 by Cys392 can lead to the extension of the original hydrogen bond and the formation of a new steric hindrance, which affected the stability of the protein structure.Conclusion:The c.1258G>T heterozygous missense mutation in exon 8 and the c.4797delG heterozygous deletion mutation in exon 14 of the F5 may be responsible for the decrease of FⅤ levels in this family.