SUMMARYObjective: Blood group is a classification of human blood based on the antigenic types on the surface of red blood cells (erythrocytes). ABO and Rh blood group systems are widely used in our country and in the world. We aim to determine distribution of the ABO and Rh blood groups in our region using the results of blood group tests studied by the blood/transfusion center of Cumhuriyet University Hospital in our study. Method: The blood groups of 99.207 subjects were examined based on data obtained blood/transfusion center admitted to the in our hospital between January 2009 and December 2013 in a five-year period as retrospectively. The blood groups was determined using tube agglutination method, microcolon method and microplate automatic blood group method in EDTA-containing blood samples and the weak D was studied in subjects with Rh factor negative. Subjects are evaluated only once for blood group during the study period. Repeated examples belong to the same individuals were excluded from the study. Results: The rates of the blood groups were determined as 43.8% A, 31.8% O, 16.4% B and 8.0% AB according to the results of our region in the study period. In addition, 87% of subjects was Rh positive and 13% was Rh negative. Most common blood group was A Rh positive (37.9%) while the least common type was AB Rh negative (1%) in our region. Conclusion: Blood is vital for the human body. Blood groups may vary between regions. Therefore, regional data must be determined and to be updated with specific time intervals. Distribution of blood groups in our blood/transfusion center is compatible with distribution of blood groups in Turkey. In addition, statistics of blood group distribution should be reviewed and critical level of blood group stock should be determined by the authorites of blood/transfusion center. Keywords: AB0 blood group system, Rh factor, Sivas.