Small-angle scattering is one of simplest methods to evaluate the average size and volume fraction of precipitates in the metals and alloys. The accuracy of the evaluated size is higher than 5 % if the analysis is proceeded in the proper way. In comparison with powder diffraction, however, there are some differences in the way to measure and analyze the small-angle scattering although the principle of the phenomena are same in both way. The key issues for measurements and analysis of small-angle scattering are overviewed and the results for high nitrogen martensitic steel are shown as an example.