This paper describes a new formulation of magnetic nanoparticles coated by a novel polymer matrix-O-Carboxylmethylated Chitosan (O-CMC) as drug/gene carrier. The O-CMC magnetic nanoparticles were derivatized with a peptide sequence from the HIV-tat protein and transferrin to improve the translocational property and cellar uptake of the nanoparticles. To evaluate the O-MNPs-Tat-Tf as drug carriers, Methotrexate (MTX) was incorporated as a model drug and MTX-loaded O-MNPs-Tat-Tf with an average diameter of 75nm were prepared and characterized by TEM, AFM and VSM. The cytotoxicity of MTX-loaded O-MNPs-Tat-Tf was investigated with C6 cells. The results showed that the MTX-loaded O-MNPs-Tat-Tf retained significant antitumor toxicity; additionally, sustained release of MTX from O-CMC nanoparticles was observed in vitro, suggesting that the O-MNPs-Tat-Tf could be a novel magnetic targeting carrier. We also studied the ability of O-MNPs-Tat-Tf crossing BBB in rats by single photon emission computed tomography (SPECT). This paper describes a new formulation of magnetic nanoparticles coated by a novel polymer matrix-O-Carboxylmethylated Chitosan (O-CMC) as drug / gene carrier. The O-CMC magnetic nanoparticles were derivatized with a peptide sequence from the HIV-tat protein and transferrin to improve the translocational property and cellar uptake of the nanoparticles. To evaluate the O-MNPs-Tat-Tf as drug carriers, Methotrexate (MTX) was incorporated as a model drug and MTX-loaded O-MNPs- Tat-Tf with an The diameter of 75 nm were prepared and characterized by TEM, AFM and VSM. The cytotoxicity of MTX-loaded O-MNPs-Tat-Tf was investigated with C6 cells. The results showed that the MTX-loaded O-MNPs-Tat- Significant antitumor toxicity; furthermore, sustained release of MTX from O-CMC nanoparticles was observed in vitro, suggesting that the O-MNPs-Tat-Tf could be a novel magnetic targeting carrier. Tf crossing BBB in rats by single photon emission com puted tomography (SPECT).