Objective: To investigate the K562 cells biological function and related molecular changes in PTEN-PI3K/AKT signaling pathway of leukemia K562 cells by inhibiting the miRNA-21 expression to explore its pathogenesis of leukemia. Methods: The chemical synthetic miRNA-21 inhibitor was transfered into K562 cells by electrotransfection. RT-PCR was used to detect the miRNA-21 expression changes. Cell proliferation and apoptosis were determined by using MTT and flow cytometry. Western-blot were used to detect the protein expression changes of PTEN, PI3K and p-AKT respectively. Results: The relative expression of miRNA-21 in experimental group was (8.070 ± 5.138)% at 24 hours, which was lower than control groups (P<0.05). The apoptotic rate of (13.370±0.250)% at 24 hours in experimental group was obviously higher than control groups. The cellular proliferation were significantly different at 24 hours. The proliferation inhibition rate was (8.1±0.9)% at 24 hours, which was up to (43.1±2.1)% at 60 hours, but the control groups showed no difference. K562 cell proliferation significantly decreased, while cell apoptosis markedly increased by inhibiting miRNA-21 expression (P<0.01). Western-blot analysis revealed up-regulation of PTEN and down-regulation of PI3K and p-AKT protein expressions after successfully suppressed miRNA-21 expression (P<0.01). Conclusion: Inhibiting miRNA-21 expression in K562 cell could suppress the PI3K/AKT pathway by up-regulation of PTEN expression and promote cell antiproliferative and pro-apoptosis effects.