A spacer includes a base, at least a supporting column, and at least a clamp. The base includes at least a bridge-shaped portion and at least a flat portion. The bridge-shaped portion includes a bridge top surface, and two curving sidewalls respectively extend from two ends of the bridge top surface and connect with the flat portion. The supporting column is disposed on the bridge top surface of the base. The clamp is disposed on the flat portion of the base. A backlight module using the same spacers is also provided. The backlight module has a reflective plate having a plurality of projections parallel to linear light sources. The spacers are coupled to the projections and support a diffusing plate. Curving sidewalls of the spacers and the adjacent curving surface of the projections facing the corresponding light sources would give the present spacer and backlight module have good optical uniformity.