The　internal　relative　humidities　of　concrete　using　different　types　of　ceramsites　with　different　prewetting　degrees　were　monitored　by　humidity　sensors.　The　study　reveals　that　the　internal　relative　humidity　of　concrete　using　low　water　absorption　rate　ceramsites　declines　more　slowly　than　that　of　concrete　using　high　water　absorption　rate　ceramsites　when　not　prewetting;　the　internal　relative　humidity　of　concrete　using　high　water　absorption　rate　ceramsites　is　higher　than　that　of　concrete　using　low　water　absorption　rate　ceramsites　when　their　prewetting　degrees　(1h　or　24h)　are　the　same;　the　internal　relative　humidity　of　concrete　using　ceramsites　is　higher　than　that　of　ordinary　concrete,　whether　the　ceramsites　are　prewetted　or　not.　©　(2011)　Trans　Tech　Publications,　Switzerland.