Since 2019, Korea Aerospace Research Institute (KARI) has been developing a main oxidizer shutoff valve (MOV) for space launcher’s 7 ton thrust liquid engine. In this study, various attempts were made to reduce the weight of the MOV by applying additive manufacturing (AM) technology rather than conventional manufacturing methods that used machining and welding, and finally achieved a weight reduction of 15%. For AM application, research on improvement in the flow efficiency inside the MOV, removal of unnecessary structures for integrated manufacturing, application of improved materials, heat treatment, and post-process technology were conducted. This study confirmed that best weight reduction effect could be expected when AM was applied to space launch vehicle parts operating in extreme vibration and cryogenic environments.