The aim of this study was to examine the effect of estrogen on fibrinogen clotting time in rabbit model experimentally, The study was performed on 14 white New Zealand race female prepubertary rabbits at two months old weighing meanly 1.4+/-0.3 kg. Blood samples was taken from ear veins of the rabbits and first fibrinogen clotting time levels were measured to obtain control values. Next day, female sex hormone preparate estradiol valerinate at a dose of 0.3 mg/kg were injected to the rabbits IM. In their examinations made on 10(th) day of injection, they were evaluated as in oestrus and under the maximal effects of estrogen, acid their blood samples were taken again to measure their fibrinogen clotting time levels. Fibrinogen clotting time levels were determined from blood samples taken before and after female sex hormone administration. Samples taken from ear veins of the rabbits were used for measurement of fibrinogen clotting time. In the study, fibrinogen clotting time values were found meanly 18.13+/-1.00 sec. from blood samples taken before estrogen injection versus 18.87+/-0.61 sec. from blood samples after 10 days of estrogen injection, in statistical assessment performed, there were not statistically significant differences (t=0.94, p>0.05) between fibrinogen clotting time values before and after estrogen administration. Our data revealed that estrogen administration caused a silghtly but insignificantly increase in fibrinogen clotting time values in the rabbits.