AbstractA tannin extract of Sanguisorba officinalis L. contains tannin in a range of 35%-100% (w/w), wherein the content of total saponin is less than 10% (w/w), and the content of sanguisorbin I is less than 5% (w/w). The extract can protect bone marrow hematopoietic stem cells, relieve the inhibition of mouse bone marrow DNA caused by drugs for radiotherapy and chemotherapy, as well as increase numbers of leucocytes.