Osteosarcoma is the most common primary malignant bone tumor with origin in the osteoid tissue producing immature bone, in which children and young adults are the mainly affected. Thus, there is an increasing need to pursue and to develop new therapeutic approaches for osteosarcoma, avoiding the limitations of the current treatments available. In this sense, the application of a gene therapy strategy and a synergistic action using chemotherapeutic agents arises as a promising therapy for osteosarcoma. Thereby, the main goal of this project is to create an antitumoral strategy for osteosarcoma, based on the development and characterization of a new, efficient and specific micellar nanocomplex that are able to encapsulate and deliver specific genes that are down-regulated in osteosarcoma, namely the miR-145 and the gene RB1, promoting an overexpression of the retinoblastoma protein (pRb) and miR-145, inhibiting the pathways involved in the invasion and proliferation of osteosarcoma cells. Therefore, it will be used plasmids with the genes that encodes for pRb and miR-145 and it will be evaluated the nanocomplex ability to transfect the target cells efficiently in osteosarcoma cell lines and in an animal model. In addition, a combined therapy will be implemented to evaluate the capability of this nanosystem to perform a synergistic action with chemotherapeutic drugs.