In the last years, miRNAs have been associated with molecular pathways of cancer and other diseases. The change of expression level of miRNA has an inhibitory role in tumorigenesis. Nevertheless, the poor bioavailability of miRNA due to the rapid enzymatic degradation is a critical handicap in cancer therapy. In this study, we designed dextran-coated iron oxide-based nanoparticle for the delivery of miR-29a to breast cancer cells and analyzed its therapeutic efficacy in vitro. Results indicated that the presence of dextran-coated magnetic nanoparticles, loaded with miR29a, enhanced the selective delivery of miR-29a. Further, miR-29a complex nanoparticles caused down-regulation of anti-apoptotic genes. These results pave the way for further investigations into the possible use of miR-29a complex magnetic nanoparticles for breast cancer therapy.