A bicycle warning lamp adapted to be mounted on each of two handlebars of a bicycle, wherein each handlebar has a hollow bar, a connection end and a free end, the connection end is connected to a frame of the bicycle, and the free end is opposite to the connection end, characterized in that the warning lamp comprising: a body having: a holding portion adapted to mount around the hollow bar of each handlebar of the bicycle and having: an inner end adapted to correspond to the connection end of the handlebar; and an outer end adapted to correspond to the free end of the handlebar; and a cap portion connected with the outer end of the holding portion of the body and having: a mounting chamber defined inside the cap portion; two partition plates, each partition plate mounted inside the cap portion to define an insertion room in the mounting chamber and between the inner wall of the cap portion and the partition plate; and two see-through portions oppositely formed on a periphery of the cap portion; a circuit board mounted inside the mounting chamber of the cap portion; two flexible printed circuit board, each FPC board mounted inside the one of the two insertion rooms in the cap portion, electrically connected to the circuit board, and having multiple light-emitting diodes (LEDs) mounted on the FPC board, wherein the FPC boards are mounted on the inner wall of the cap portion according to curvature of the inner wall of the cap portion for the LEDs on the FPC boards to be attached to and align with the see-through portions of the cap portion and light emitted from the two FPC boards passes through the see-through portion and directs to a forward direction and a backward direction; a power supply electrically connected to the circuit board to supply power to and light up the LEDs of the FPC boards; and a control switch mounted on the holding portion of the body, and electrically connected to the circuit board to control the FPC boards to turn on or off. a body having: a holding portion adapted to mount around the hollow bar of each handlebar of the bicycle and having: an inner end adapted to correspond to the connection end of the handlebar; and an outer end adapted to correspond to the free end of the handlebar; and a cap portion connected with the outer end of the holding portion of the body and having: a mounting chamber defined inside the cap portion; two partition plates, each partition plate mounted inside the cap portion to define an insertion room in the mounting chamber and between the inner wall of the cap portion and the partition plate; and two see-through portions oppositely formed on a periphery of the cap portion; a holding portion adapted to mount around the hollow bar of each handlebar of the bicycle and having: an inner end adapted to correspond to the connection end of the handlebar; and an outer end adapted to correspond to the free end of the handlebar; and an inner end adapted to correspond to the connection end of the handlebar; and an outer end adapted to correspond to the free end of the handlebar; and a cap portion connected with the outer end of the holding portion of the body and having: a mounting chamber defined inside the cap portion; two partition plates, each partition plate mounted inside the cap portion to define an insertion room in the mounting chamber and between the inner wall of the cap portion and the partition plate; and two see-through portions oppositely formed on a periphery of the cap portion; a mounting chamber defined inside the cap portion; two partition plates, each partition plate mounted inside the cap portion to define an insertion room in the mounting chamber and between the inner wall of the cap portion and the partition plate; and two see-through portions oppositely formed on a periphery of the cap portion; a circuit board mounted inside the mounting chamber of the cap portion; two flexible printed circuit board, each FPC board mounted inside the one of the two insertion rooms in the cap portion, electrically connected to the circuit board, and having multiple light-emitting diodes (LEDs) mounted on the FPC board, wherein the FPC boards are mounted on the inner wall of the cap portion according to curvature of the inner wall of the cap portion for the LEDs on the FPC boards to be attached to and align with the see-through portions of the cap portion and light emitted from the two FPC boards passes through the see-through portion and directs to a forward direction and a backward direction; a power supply electrically connected to the circuit board to supply power to and light up the LEDs of the FPC boards; and a control switch mounted on the holding portion of the body, and electrically connected to the circuit board to control the FPC boards to turn on or off.