Abstract: Using sheep antihuman IgG serum labelled with fluorescein-iso-thiocyanate ,the human IgG in bloodstains could be found. The positive result could be acquired even with a few micro-fibrin torn from a 1-cm long sauge fiber stained with 2-ul of 1:100 diluted blood (1:200 diluted serum). That means the stains containing only one-thousandth micro gram of serum protain could be identified by this method. 127 human bloodstains within five years old and eleven bloodstains of eleven kinds of animals were tested and all the results were correct.The blind test of 90 bloodstains (human, 55, animai,35) got 88 correct conclusion (97.78%) and 2 misjudgement(2.22%) . The species identification of blood stain using the immunofluorescence techque is a nice me-theod with high sensitivety and specifificity.