Molecular dynamics simulation enables us to sample dynamic structures of biomolecules with high spatio-temporal resolution. However, due to the difficulties of reproducing the real ensemble from MD simulation, it is important to compare with experimental data. Among various experimental methods, Small-angle X-ray scattering (SAXS) can provide information on structural ensemble in solution at ambient temperature without any observational bias, even though structural information encoded in the profile is limited to low-resolution. In fact, SAXS data can also reveal a variety of molecular properties. In this talk, the principle of the measurement and analysis will be briefly explained, and then the study of molecular dynamics using SAXS and MD calculations will be presented.