In a light source apparatus, a method of manufacturing the light source and a backlight assembly having the same, a light guide plate (LGP) includes an upper surface and a lower surface facing each other and a first side surface and a second side surface. The light source is placed in the LGP adjacent to the first side surface and emits light toward the second side surface. The power supply unit is electrically connected to the light source and partially placed in the LGP. The light source may include a lamp or a light-emitting diode (LED). The power supply unit may include a wire or a power supply substrate. The light source apparatus may be formed by an injection molding process using lower and upper mold frames. Therefore, backlight assembly size, the number of parts and manufacturing steps may be decreased, and the illumination quality may be improved.