This study is to investigate the anti-tumor effect in vitro of methotrexate modified by LH-RH peptide (LH-RH－MTX).  LH-RH receptors highly expressing MCF-7 human breast carcinoma cell line and lowly expressing K562 human erythroleukemia cell line were served as the tested cells.  The cell proliferation inhibition rates of LH-RH－MTX were detected by MTT colorimetric assay.  The effects of LH-RH－MTX on the cell cycle and apoptosis rates were detected by flow cytometry.  The inhibition rate of LH-RH－MTX on MCF-7 cells was much higher than that on K562 cells, and the inhibition rate of LH-RH－MTX on MCF-7 cells was much higher than that of free MTX at the same concentration.  The inhibition rate of LH-RH－MTX on rat bone marrow mononuclear cells was less than that of free MTX.  The number of MCF-7 cells in S phase increased after administration of LH-RH－MTX.  The apoptosis rate of LH-RH－MTX group significantly increased compared with that of the control group and MTX group.  The relative expression of LHRHR mRNA of LH-RH－MTX group markedly decreased compared with that of the control group and MTX group.  LH-RH－MTX is realizable to reduce drug side effects, increase the therapeutic index and achieve tumor-targeted therapy.