Thermally　driven　moisture　and　vapor　transport　in　unsaturated　soil　under　a　thermal　loading　applied　by　underground　structures　affects　the　magnitude　and　distribution　of　matric　suction.　There　is　a　lack　of　data　about　the　temperature　dependency　on　the　hydraulic　conductivity　function　(HCF).　This　study　(1)　developed　and　used　a　temperature-controllable　soil　column　for　directly　and　simultaneously　measuring　the　temperature　dependency　on　both　the　soil-water　retention　curve　(SWRC)　and　HCF　using　the　instantaneous　profile　method,　and　(2)　conducted　water-vapor　heat　transport　analyses　to　illustrate　the　effects　of　temperature　dependency　of　SWRC　and　HCF　on　matric　suction.　The　measurements　showed　that　for　sand　there　was　a　suction　threshold　of　2　kPa,　below　which　the　hydraulic　conductivity　of　sand　heated　to　50　degrees　C　became　higher　than　that　at　20　degrees　C　due　to　decreased　water　viscosity.　Above　this　threshold,　the　hydraulic　conductivity　at　50　degrees　C　became　lower,　by　as　much　as　an　order　of　magnitude　at　10　kPa　suction,　because　of　temperature-induced　reduction　of　water-retention　ability.　A　parametric　study　revealed　that　using　SWRC　or/and　HCF　obtained　at　20　degrees　C　overestimated　the　magnitude　of　suction　for　soil　heated　to　a　temperature　higher　than　20　degrees　C.　The　overestimations　were　greater　when　heating　took　place　in　drier　soil.　The　effects　of　vapor　transport　were　negligible　during　the　early　stage　of　heating,　and　became　prominent　only　after　7-8　days　of　continuous　constant　heating　of　the　soil,　regardless　of　the　amount　of　initial　soil　suction　considered.