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°C　became　higher　than　that　at　20°C　due　to　decreased　water　viscosity.　Above　this　threshold,　the　hydraulic　conductivity　at　50°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°C　overestimated　the　magnitude　of　suction　for　soil　heated　to　a　temperature　higher　than　20°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.　©　2020　American　Society　of　Civil　Engineers.