Media-based　modulation　(MBM)　is　a　recently　proposed　modulation　scheme　which　has　the　advantages　of　increased　spectral　efficiency　and　improved　performance.　In　this　paper,　a　physical　layer　security　(PLS)　scheme　is　proposed　for　the　multiple-input　multiple-output　(MIMO)　media-based　modulation　system　using　generalized　spatial　modulation　(GSM)　to　resist　the　passive　eavesdropping　from　a　multiple-antenna　eavesdropper.　Secure　mapping　rules　between　the　information　bits　and　the　transmit　patterns　are　designed　based　on　the　abundant　legitimate　channel　realizations　of　the　MIMO　MBM　system.　Due　to　the　independent　fading　of　the　legitimate　link　and　the　eavesdropping　link,　the　designed　mapping　rules　are　unavailable　and　appear　random　to　the　eavesdropper.　Therefore,　the　correct　detection　of　the　information　bits　at　the　eavesdropper　is　prevented,　which　is　validated　through　bit　error　rate　(BER)　analysis　and　simulations.　The　ergodic　secrecy　rate　is　analyzed　and　a　tight　closed-form　approximation　is　derived.　Simulation　results　show　that　the　proposed　secure　GSM　MBM　scheme　outperforms　the　existing　secure　MBM　schemes　without　consuming　jamming　power　or　requiring　eavesdropper＇s　channel　state　information.　©　2013　IEEE.