Abstract: About how the prokaryotic ancestor molecular of core histones evolved into four kinds of core histones of eukaryote has two possibilities:one is the ancestral molecular had already differentiated into four kinds at stage of prokaryote,the other is this differentiation occurred after the cell evolving into the eukaryotic cell.HMf and HMt,two kinds of histone-related proteins,isolated respectively from Methanothermus fervidus and Methanobacterium thermoautotrophicum △H,Archaebacteria which are most closely related to eukaryote,by reeves laboratory have already differentiated into HMf1,HMf2 and HMt1,HMt2.Up to now,the core histones found from lower eukaryotic cell,such as Leishmania and Tetrahymena,have all differentiated into four kinds.In this paper,the total histones were prepared from Giardia lamblia,the most primitive eukaryotic cell,by engaging in methanol prefixation,two times of 0.3 mol/L HCl extraction,acetone precipitation and DNA affinity chromatography.The results of electrophoresis,SDS gel and acid urea gel,of the Giardia histones showed that seven major protein bands could be resolved,and five of these bands migrated to position similar those of five kinds of calf thymus histones.It seems,therefore,that the Giardia histones have already differentiated and consisted of at least five kinds of histones,and,on certain extent,this supported the hypothesis that the histone had already differentiated into four different kinds at the stage of prokaryotic ancestor of eukaryote.