Recycling copper slag to recover metals has been focused on copper, which is contained in the range of 0.77 to 1.32%; however some slags also contains molybdenum in amount up to 0.4% transforming the copper smelting slags into a potential raw material for the development of new processes to obtain new products. In this regard, copper slags were treated using roasting-leaching process in order to recover the molybdenum content in the slag. Oxidative roasting is used to convert the iron oxide into insoluble hematite, and copper and molybdenum into the soluble form in acidic solution. Since molybdenum is associated to iron oxide spinel type phase, its recovery was influenced by the magnetite content in the slag during the leaching process. Sulphuric acid was used for leaching the slag, and molybdenum shows recovery higher than 80%. Thus, the obtained results show the feasibility for recovering molybdenum using two-step processes, oxidative roasting followed by an acidic leaching. © 2010 Maney Publishing.