The key to successful gene therapy is to find a suitable method and carrier for transfection to allow a gene to be transferred into a cell and integrated into the target gene. The aim of this study was to determine whether biomagnetic material could be combined with the nucleic acid for gene transfection. Dextran-coated iron oxide nanoparticles (DCIONPs) were prepared and mixed with the plasmid pGenesil-1 containing the test gene, which expresses enhanced green fluorescent protein (eGFP). PGenesil-1 empty vector was used as a control. The binding ability was assessed by electrophoresis of the DNA on agarose gels and quantification using BANDSCAN software. Using different gene carriers, Lipofectamine 2000, Sofast, and DCIONPs, the large intestine cancer (Lovo) cell line was transfected with or without a magnetic field. The expression of eGFP was observed by fluorescence microscopy, and the transfection efficiency was compared. The results showed there was a rapid increase in combining rate when the quality ratio of DCIONPs and pGenesil-1 ascended from 1∶1 to 5∶1. However, the combining rate increased less rapidly as the quality ratio continued ascending. The expression of eGFP showed that the early transfection rate could be improved by applying a magnetic field. In conclusion, the DCIONPs we synthesized are able to carry plasmid DNA and enhance the early transfection efficiency when using a magnetic field.