The　water　absorption　and　desorption　process　of　different　prewetting　degree　ceramsites　embedded　in　ceramsite　concrete　was　obtained　by　a　U-tube　micro　pressure　measurement　device.　The　internal　relative　humidities　of　ceramsite　concrete　using　different　prewetting　degree　ceramsites　were　monitored　by　humidity　sensors.　The　study　reveals　that,　with　the　increase　of　ceramsite　prewetting　degree,　the　internal　relative　humidity　of　ceramsite　concrete　increases　because　the　reservoir　function　of　ceramsite　is　more　obvious.　©　(2011)　Trans　Tech　Publications,　Switzerland.