Objective To analyze the effects of an inhibitor of the SH3 (Src homology) domains of Grb2 on the growth and proliferation of K562 cells. Methods The peptidimer [(VPPPVPPRRR)2-K], penetratin (RQIKIWFQNRRMKWKK) and peptidimer-c [poptidimer linked to penetratin: (VPPPVPPRRR)2-K-Aha-RQIKIWFQNRRMKWKK] were synthesized by solid-phase synthesis using Fmoc chemistry, and purified by high performance liquid chromatography (HPLC) on a C18 column. Purity was evaluated by HPLC, and the identity of the peptides was checked by electrospray mass spectroscopy (MS). A pull-down assay was used to observe the specific binding of peptidimer-c to the Grb2 of K562 cell lysates. The inhibition of peptidimer-c on K562 cell proliferation was evaluated by trypan blue exclusion assay, the cytostatic effect was tested by clonogenic assay, and the cytotoxicity was examined by WST-1 method. A further experiment was performed with clonogenic assay to analyze the co-effect of peptidimer-c respectively combined with Gleevec, Hydroxyurea and Cytarabine by Jing's method. Results The HPLC analysis showed only a simple peak, which means that the peptide is in high purity. MS analysis showed the peptides were coincided with the design. The molecular weight of peptidimer-c was of 4794.0 and that of the penetratin 2246.7. Pull-down assay demonstrated that the peptidimer-c, not the penetratin, could bind to Grb2 specifically. The trypan blue assay showed that the peptidimer-c could inhibit the proliferation of K562 significantly in a dose-dependent manner, even 3～6 h after the cells were exposed to the drug, and penetratin alone did not influence the cell proliferation. Gleevec inhibited the growth of K562 not only in a dose-dependent manner, but also in a time-dependent manner. WST-1 test showed the cytotoxieity of peptidimer-c or Gleevec on K562 cells, the IC50 of peptidimer-c was (17±2) μmol/L and the IC50 of Gleevec was (0.25±0.05) μmol/L. In the methylcellulose semi-solid medium system, the colony formation of K562 was greatly decreased by peptidimer-c as compared to the penetratin, and the colony number decreased as the dose of peptidimer-c increased. The IC50 value ofpeptidimer-c on K562 colony formation was (3.9±0.9) μmol/L, IC50 of Gleevec was (0.03±0.02) μmol/L, IC50 of Hydroxyurea was (15±7) μmol/L, and that of cytarabine was (0.014±0.012) μmol/L. There were synergistic effects of peptidimer-c with Gleevec, Hydroxyurea or Cytarabine on K562 by colonogenic assay. Combination of 1.5 μmol/L peptidimer-c and 0.05 μmol/L Gleevec showed synergistic effect on K562, as well as the combination of 1.5 μmol/L peptidimer-c and 0.006 μmol/L or 0.01 μmol/L Cytarabine. Conclusion These results suggested that peptidimer-c had an inhibitory effect on K562 cells and combination of peptidimer-c with other drugs would increase the anti-cancer effects.