An LED module includes a light bar and a fixing device. The light bar includes a supporting plate and a circuit board mounted on the supporting plate. The circuit board has a plurality of light emitting diodes thereon. The supporting plate includes a first tongue and a second tongue respectively extending from two opposite ends thereof. The fixing device includes a substrate to support the light bar, a fastening piece and a tenon fixing respectively the two ends of the light bar on the substrate. The fastening piece includes a seat fixed on the substrate and a locking arm connecting to the seat. The first tongue of the light bar is embedded in the tenon, and the second tongue of the light bar is received in a space defined between the seat and the locking arm.