Abstract: Objective To construct a subtracted cDNA library of differentially expressed genes in eosinophifs from asthma patients. Methods Suppression subtractive hybridization (SSH) was used to isolate the cDNA fragments of differentially expressed genes in the eosinophils of asthma patients before and after treatment. The cDNA fragments were directly inserted into T/A cloning vector to establish the subtractive library, followed by amplification of the library through E. coli transformation with calcium chloride and screening of blue and white clones of the transformants. One hundred positive bacterial clones were randomly picked and identified by colony PCR. Results The amplified library contained more than 3 000 positive bacterial clones. Analysis of the randomly selected 100 white clones by PCR showed that 90% of the clones contained 100-500 bp inserts, which might be the cDNA fragments of differentially expressed genes in eosinophils of asthma patients before treatment. Conclusion A subtracted cDNA library of differentially expressed genes in the eosinophils of asthma patients before and after treatment is constructed successfully by SSH and T/A cloning techniques, which lays a solid foundation for screening and cloning new specific differentially expressed genes in the eosinophils of asthma patients.