An adhesive optical fiber device for aquarium has a light-emitting device and a light-guiding optical fiber device. The light-emitting device and the light-guiding optical fiber device include respectively a first magnetic device and a second magnetic device. The light-emitting device and the light-guiding optical fiber device are disposed on the outer and inner surfaces of a sidewall of the aquarium, respectively, and fixed thereon due to the attraction between the first magnetic device and the second magnetic device. The light source of the light-emitting device aims at a light entrance of the light-guiding optical fiber device, so that the optical fiber cores of the light-guiding optical fiber device can transmit light and emit light on their free ends. The optical fiber cores in the aquarium can be distributed by demand to decorate the aquarium.
