OBJECTIVE To detect and analyze coagulation related indexes and genotypes of a patient with congenital fibrinogen deficiency and his family members, and to investigate the possible molecular pathogenesis. METHODS Four peripheral blood samples (proband and 3 family members) were collected and the prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen (Fg), D-Dimer and eight coagulation factor indicators were detected. All exons and flanking sequences of the FGA, FGB, and FGG genes encoding the three peptide chains of fibrinogen were sequenced and analyzed by bioinformatics. RESULTS Among the eight coagulation factors of the proband and the elder sister, F Ⅴ and F Ⅷ were slightly higher, TT was significantly prolonged, and Fg was significantly reduced. Sequencing results showed that c.901C>T heterozygous mutation existed in the FGG gene. Bioinformatics analysis showed that the mutation changed the original protein structure and reduced the number of hydrogen bonds. CONCLUSIONS The fibrinogen gamma chain c.901C>T heterozygous mutation is the main cause of congenital fibrinogen deficiency in this family. This mutation is reported for the first time at home and abroad.