In this paper, we discuss the effiectiveness of magnesium alloys through practical space applications in which we have developed a few small-sized space systems mid have used magnesium alloys in order to reduce the total mass of the systems. We introduce three examples of our developed systems. The first one is a CanSat whose is a pico-satellite sized of 350ml can, less than 350g in mass, and the second one is a small docking mechanism in order to grasp and guide a micro satellite for a small mothership-daughtership satellites formation flying in orbit The last one is a CubeSat whose is a pico-satellite sized of 10cm*10cm*10cm, less than 1kg in mass and is planned to launch into a Low Earth orbit Outline description of the systems is given, and design restrictions against magnesium alloys and the mass reduction effect compared with aluminum. alloys are discussed. Also, issues of manufacturing, processing and surface treatment for the elaborate magnesium parts are explored.