AbstractAggregates of nanodiamond particles dispersed in polar liquids (H2O and DMSO) upon undergoing a special milling procedure are studied by small-angle neutron scattering at a scale of 1−100 nm. The size and fractal character of the aggregates as well as the structural features of nanodiamond particles (size, surface) are compared for both solutions. The structural difference between liquid dispersions and initial nanodiamond powder is analyzed. The concentration effect is followed within an interval of 0.2−10 wt % to conclude about the interaction of the aggregates. It is shown that the developed structure of the aggregates allows their interpenetration in concentrated solutions. The contrast variation procedure using mixtures of nondeuterated and deuterated solvents is performed to judge the homogeneity of the aggregates and to find out their mean scattering length density. The existence of a nondiamond component in the particles is discussed on the basis of the scattering data.