Objective The kinetics, affinity and specificity between the human C5a anaphylatoxin and it's antisense peptide R4 was observed. Methods The antisense peptide R4 was in immobilization, and the rhC5a a nd the sense peptide (L2) of the C5a (that amino acid sequense is VNNDETCEQRAAR) was in streaming movement. The kinetic rate and equilibrium binding constants f or their interaction by using Biomolecular interaction analysis(BIA). Re sults The antisense peptide R4 can bind to anaphylatoxin C5a and its co rresponding sense peptide L2 selectively. The dissociation equilibrium constants ( K D) between R4 and rhC5a is 6.62×10 -6 mol and the K D betwee n R4 and L2 is 4.508× 10 -6 mol. Conclusion There are biospecific interactions between anaphylatoxin C5a and its anti sense peptide. So it is available to study the interactions between the peptide and it's antise nse peptide by using the optic Biosensor.