A table lamp with a rotatable lamp casing includes a base and an arm extended from the base. The arm has one end connected to the base and the other end connected to an assembling portion. A luminant portion is mounted on the assembling portion. The luminant portion has a seat mounted on the assembling portion and a lamp mounted on one side of the seat. A transparent casing is rotatably mounted on the assembling portion and covers the luminant portion. The casing has multiple light-guiding sections disposed therein. Each light-guiding section provides a specific illuminant mold.