Efficient DNA condensation and decondensation, as well as low toxicity, are required for an efficient gene delivery vehicle. We report on the condensation of DNA by a mixture of cationic agents, low-molecular-weight polyethylenimine (PEI, 1.2 KDa) and Fe(III) ions, and respective decondensation, using experimental and theoretical methods. It was found that a significant reduction in the amount of PEI necessary to induce DNA condensation is achieved by the addition of the trivalent ions, which are very inefficient on their own. In addition, the mixture makes DNA decompaction by heparin easier, starting from similar degrees of condensation. The results obtained using simulations of coarse-grain models are coherent with those obtained experimentally. It was also found that the improved effect of the multivalent ions is related to the preferred positioning of the trivalent ions in the DNA areas less populated by the polycation chains, in between the polycation chains and at the ends of the DNA, which facilitates the overall condensation.