A sandwich aptamer-based chemiluminescence(CL) biosensor for sensitive determination of cocaine was developed based on magnetic microspheres as a special biomolecule immobilizing carrier.The experimental parameters,including amounts of magnetic microspheres,capture DNA,cocaine-binding aptamer,reporter DNA probes and dilution coefficient of SA-HRP were optimized .Under the optimized conditions,a good linear relationship was obtained between CL intensity and logarithms of cocaine concentration from 1.0×10-8mol/L to 1.0×10-4 mol/L (r2=0.989 7).The detection limit was 3.2×10-9 mol/L.To assess the CL aptasensors′ability to detect cocaine in complex samples, the specific recognition ability of cocaine aptasensors in the presence of human blood serum was also tested.The method showed a good selectivity.