Objective To conclude the characteristics of clinical usage of unprocessed rehmannia root since the Han Dynasty and to provide a basis for the formulation strategy of its clinical dosage. Methods A database including dosage of unprocessed rehmannia root of every past dynasty was established by selecting medical literatures that are most representitive of each dynasty and entering the name

overall dosage

dosage of unprocessed rehmannia root

number of Chinese medicinals

volume of water added

administration method of all formulas with unprocessed rehmannia root successively. Frequency of occurrence

dosage most commonly used

upper limit of dosage

lower limit of dosage

maximum dosage

minimum dosage and average dosage of unprocessed rehmannia root were caculated. The characeristic of dosage for past dynasties was analyzed with literature. Results In Han and Tang dynasty

unprocessed rehmannia root was used in high dose（ > 41. 4 g） and in a wide range. However

from Song dynasty till nowadays

dosage of unprocessed rehmannia root has been fluctuating yet remained in a lower level

casting as decreased average dosage and dosage most commonly used

with a narrower range of dosage most commonly used

while the range of all dosage fairly wide. Conclusion Using 25 g of unprocessed rehmannia root mainly has the effects of nourishing yin

clearing heat and cooling the blood

while usage of more than 30 g has the effects of dispelling rheumatism and calming the mind.