This　paper　presents　an　investigation　of　wave　transmission　in　complex　rock　masses;　the　rocks　have　different　wave　impedances　on　either　side　of　a　joint　The　conventional　displacement　discontinuity　method　was　modified　for　complex　rock　mass　wave　propagation　by　introducing　four　sets　of　characteristic　lines.　Two　cases,　＂soft-to-hard＂　and　＂hard-to-soft＂　rock　masses,　were　used　to　demonstrate　wave　propagation　through　the　complex　rock　masses.　The　results　show　that　the　wave　impedance　ratio　plays　an　important　role　in　the　wave　propagation　through　the　complex　rock　masses.　For　the　case　of　＂soft-to-hard＂　rock　masses,　the　particle　velocity　transmission　ratios　are　always　smaller　than　1.0,　while　the　stress　transmission　ratios　may　be　larger　than　1.0　when　the　wave　impedance　ratio　and　the　frequency　of　the　incident　wave　are　sufficiently　small.　On　the　other　hand,　for　the　case　of　＂hard-to-soft＂　rock　masses,　the　stress　transmission　ratios　are　always　smaller　than　1.0,　while　the　particle　velocity　transmission　ratios　may　be　larger　than　1.0　when　the　wave　impedance　ratios　are　sufficiently　large　and　the　frequencies　of　the　incident　wave　are　sufficiently　small.　The　phenomenon　indicates　that　wave　propagation　in　complex　rock　masses　is　not　always　attenuated　but　may　actually　be　enhanced　in　some　cases.