Ride　comfort　can　be　affected　by　the　multi-axis　vibrations.　This　research　was　designed　to　investigate　how　the　seat　transmissibility　was　affected　by　the　variation　of　single-axis　vertical　vibration　and　dual-axis　horizontal　and　vertical　vibration.　Twelve　occupants　were　exposed　to　vertical　vibration　(0.2,　0.4,　or　0.8　ms(-2)　r.m.s.)　with　and　without　additional　horizontal　vibration　(0.2,　0.4,　or　0.8　ms(-2)　r.m.s.).　The　peak　frequencies　of　both　vertical　in-line　and　horizontal　cross-axis　seat　transmissibilities　to　the　seat　back　and　the　seat　cushion　reduced　with　increasing　the　amplitude　of　single-axis　vibration　and　dual-axis　vibration.　And　the　peak　frequencies　in　the　seat　transmissibilities　measured　with　dual-axis　vibration　were　lower　than　those　measured　with　single-axis　vibration.　The　seat　transmissibilities　measured　with　dual-axis　vibration　might　exhibit　similar　resonant　behaviour　to　those　acquired　with　single-axis　vibration.　The　peak　frequencies　of　the　seat　transmissibilities　to　the　interfaces　between　seat　and　occupant　might　be　induced　by　the　same　vibration　mode.