New tungsten bronzes, MgxWO3 and MgxW18O49, have been synthetized by magnesium chemical insertion reaction. For the former case, two blue bronzes with composition Mg0.09WO3 and Mg0.15WO3 have been isolated through a topotactic reaction that keeps the parent hexagonal structure unaltered. In the case of W18O49, a new compound with composition Mg0.9W18O49 and lattice parameters close to those of W18O49 has been synthetized. We have also studied the electrochemical lithium insertion in h-MgxWO3 and MgxW18O49. In this way, different phases have been detected in the systems Li-MgxWO3 and Li-MgxW18O49 and a relationship between the maximum quantity of lithium inserted and the magnesium content is deduced and discussed in terms of the ionic potential of the intercalated ions.