A backlight module includes a light guide plate, a wavelength converter, and a light emitter. The light guide plate includes a main body, a first extension portion, and a second extension portion. The first extension portion is connected to the main body. The second extension portion is connected to the first extension portion. The wavelength converter is disposed at a side of the main body. The wavelength converter has an incident surface. The incident surface faces away from the main body. The first extension portion abuts against a sidewall of the wavelength converter. The second extension portion abuts against the incident surface. The light emitter is disposed at a side of the light guide plate.