Abstract: Disclosed is an antenna booster case for mobile devices for preventing death grip in a mobile device with an internal antenna, which has become a significant issue in recent years. More particularly, the present disclosure relates to an antenna booster case for mobile devices, which includes a case antenna provided to a protective case body, enclosing an outer surface of a mobile device, to be connected to an internal antenna of the mobile device through physical contact therewith or without physical contact therewith to enhance transmission/reception sensitivity of the mobile device. The antenna booster case includes a protective case body enclosing an outer surface of a mobile device; and a case antenna including a loop member secured to the protective case body and a connection part brought into contact with a conductive frame of the mobile device.