A bicycle light assembly includes a light shell, a light holder, a light device and a positioning element. The light shell surrounds tubes of a bicycle frame. The light shell has a locating space penetrating through the light shell in a front-to-rear direction, and an opening communicated with the locating space. The light holder is covered to a front of the opening. The light device is connected to the light holder. The light device is positioned in the locating space. The positioning element is positioned in the locating space. The positioning element has a main body. The main body is sleeved on an outer surface of the light device. The main body has a first positioning piece and a second positioning piece. The first positioning piece abuts against an inner surface of the light shell. The second positioning piece abuts against a rear surface of the light holder.