A backlight module and a display panel device using the same are provided. The backlight module includes a light source module, an open frame, and a reflector sheet. The open frame is disposed around the light source module and has a first free-end and a second free-end. A space interval exists between the first and second free-ends. The reflector sheet is disposed on a rear side of the light source module and has a body and a sidewall. The sidewall corresponds to the space interval between the first and second free-ends and extends over the light source module. The display panel further includes a liquid crystal display panel (LCD panel) on the light source module and a front frame which is disposed on the LCD panel enclosing a lateral side of the LCD panel. The sidewall of the reflector sheet extends between the lateral side of the LCD panel and the front frame to provide insulation.