To obtain the aptamers with high affinity and specificity for cyclosporin A(CsA),a synthesized 78 nt single stranded DNA(ssDNA)random library containing 35 random sequences flanked by invariant primer was subjected to 1 1 rounds of selection against CsA by SELEX protocol.Magnetic beads were used for target immobilization and the biotin-streptavidin-horseradish peroxidase system was employed for determining the binding affinity between the aptamers and CsA. After ten rounds of selection and amplification, with an increasing affinity for each round,the selected aptamers were cloned,sequenced and analyzed for their primaryand secondary structures.The 19 aptamers were divided into five groups based on primary sequence homology.Hairpin loop is the main motif in the predicted secondary structure and is supposed to be the binding part of the aptamers to CsA.The CsA-specific aptamers will be useful for enzyme-linked assays or immunofluorescence asses of CsA.