A roadside lamp with a heat dissipating design is disclosed. The roadside lamp of the present invention comprises a seat portion and a plurality of light emitting units. A panel is fitted to the seat portion and the light emitting units are fitted to the panel. The back portion of the panel is tightly fitted to a heat dissipating fin-like portion. A pair of rails extends outwardly from the fin-like portion. The pair of rails may be used to connect the roadside lamp with a surface in a place such as a tunnel. For example, a track may be provided on the top portion of a tunnel; therefore, a plurality of the roadside lamps may be fitted to the track in a tidy manner. The pair of rails allows each roadside lamp to be fitted to the track and thus, the location of the lamp may be adjusted.