Investigation on the detailed structure of bulk metallic glasses (BMGs) has become a hot research topic in recent years. It is essential for understanding the development of unique properties of BMGs, especially those showing unique thermal behaviour and good plasticity. In-situ study on structural evolution is generally lacking. In this study, we propose to use in-situ neutron diffraction technique to investigate the microstructural evolution with temperature and loading for two typical BMGs that show very similar compositions (Nb-bearing and Nb-free) but significantly different thermal and mechanical properties (with or without plasticity). The research will lead to development of fundamental insight into the origin for different thermal and mechanical behaviours of the two BMGs. It will also improve the understanding on deformation mechanisms of BMGs with or without plasticity.