Objective: To investigate the characteristics of CGI-100- knockdown K562 cells and the effect of CGI-100 RNA interference (RNAi) on matrine-treated K562 cells.Methods: Three oligonucleotides targeting CGI-100 gene and a pair of negative control containing the same nucleotide composition with a different sequence were devised and chemically synthesized. The inhibition efficiency of CGI-100 expression by shRNA-CGI-100 in K562 cells was determined using semiquantitative RT-PCR and dot blot hybridization. The effect of CGI-100 RNAi on the growth of K562 cells was examined using MTT assay and cell differentiation was measured by distinct approaches including flow cytometry, benzidine staining and electron microscope. After CGI-100-konckdown K562 cells were incubated with 0.2 mg/ml of matrine or 30 μmol/L of hemin for 48 h, the expression levels of Glycophorin A(GPA)(CD235a) and Growth factor independence-1B mRNA(Gfi-1B mRNA) were measured by RT-PCR and the protein levels of GPA, CD14 and CD15 were detected by flow cytometry.Results: The eukaryotic expression vectors of CGI-100 RNAi were successfully constructed. The K562/shRNA-CGI-100 cell line was established in which the inhibition efficiency of CGI-100 gene expression by shRNA-CGI-100 was 54%. CGI-100-knockdown inhibited the proliferation and induced erythroid differentiation in K562 cells. Compared with the control K562 ceils, the K562/shRNA-CGI-100 cells showed decreased absorbance value detected by MTT assay, decreased enchromation, increased heterochromation, increased percentage of G0/G>1 phase cells, decreased population of S phase cells, decreased PI (proliferation index of cells), and elevated percentage of benzidine-positive cells. Moreover, the sensitivity of K562/shRNA-CGI-100 cells to either matrine or hemin was enhanced and the sensitivity of these cells to matrine was higher than that to hemin. Compared with the control K562 cells, matrine treatment in K562/shRNA-CGI-100 cells resulted in increased inhibitory rate of proliferation, elevated percentage of benzidine-positive cells, obviously up-regulated mRNA expressions of GPA and Gfi-1B, and increased mean fluorescence intensity (MFI) of GPA. No CD14 expression was detected and no statistical significance was found for the detected CD15. Finally, the MFI of GPA increased in K562/shRNA-CGI-100 cells treated with hemin and was 1.7 times less than that in cells exposed to matrine.Conclusion: These results suggest that the function of CGI-100 gene is correlated with the deregulated proliferation and the block of erythroid differentiation in K562 cells and may also be involved in matrine-induced erythroid differentiation in K562 cells.