Metallic glasses (MGs) have attracted significant interest in materials science and engineering field due to their excellent mechanical properties such as high strength, elastic modulus and hardness due to their random atomic configuration. After 1990s, numerous MGs with high glass-forming ability have been developed, which enable us to them with a bulky shape and to be applied as many kinds of mechanical parts. However, a brittle nature in bulk metallic glass (BMG) has been recognized, which appears obviously by structural relaxation through low temperature annealing and/or mechanical processing. The authors have been studying a novel method of relaxation controlling, that is, a recovery of a less relaxed state (so-called as rejuvenation), using a conventional annealing treatment [1-3]. Recently, we have succeeded to control the relaxation state preciously through a rejuvenation process, which leads to improve mechanical ductility [4,5]. In this presentation, the recent results on controlling a relaxation state and an excellent ductility in Zr-based BMGs will be reported. Our results provide insights for the effect of relaxation state and bring a novel evolution in BMG and a beneficial progress for their application.