A back plate assembly and a backlight module are provided. The back plate assembly includes a back plate, at least one optical film and at least one fixing member. The back plate includes a bottom plate and a sidewall. The optical film is disposed on the bottom plate. The fixing member includes a main body and a protruding member. At least one portion of the main body overlaps with the sidewall. The protruding member is disposed on the main body and is combined with the optical film.