Abstract: In this study,the transfer factor（TF） in yak spleen was extracted by using freezing-thawing-dialysis method. The physical and chemical properties of the extracts, such as clarity and p H values, were determined and analyzed. The sterility test,pyrogen test, safety test, allergy test and in vitro antibacterial test were carried out to biologically characterize the extracted TF.The results revealed that the TF extracted by the method contained DNA and nucleotide acid, and it was germ free, non- pyrogen,non-toxic, non-allergic, non-antigenic. All of the tested indicators of the extracted TF complied with the quality standard of biological preparation. The results of the study provide experimental basis for the development and application of TF in yak spleen.