Newly prepared microcapsules with diameters of the order of 0.1 mu m have been investigated by means of static and dynamic laser light scattering, synchrotron small-angle X-ray scattering (SAXS), viscosimetry, and electron microscopy. The microcapsule has a core of phosphoric acid, bis(2 3-dibromopropyl)-2,3-dichloropropyl ester, and a wall composed of polyurethane-urea. The dispersing medium (H2O) contains copoly(vinyl alcohol-vinyl acetate) which acts as a protective colloid. Static light scattering and SAXS give the same z-average radius of gyration R(g) 110 nm in the concentration range of 1 x 10(-5)-5 x 10(-4) g/cm(3) for lightscattering and of 1 x 10(-3)-0.14 g/cm(3) for SAXS. The hydrodynamic radius R(h) = 143 nm as determined by dynamic Light scattering is close to the viscosity radius R(eta) = 151 nm obtained from intrinsic viscosity measurements of the microcapsule suspension. By assuming the microcapsule as a solid sphere, the radius of gyration estimated from R(h) was R(g,cal) = 0.78R(h) = 112 nm. The agreement of R(g) and R(g,cal) as well as R(h) and R(eta) strongly suggests that in wet form, the protective colloid has stuck tightly onto the surface of the microcapsule. The number-average radius R(n) obtained from electron microscopy was 65 nm. The radius of gyration calculated from the size distribution based on electron microscopy wasR(g,cal,e) = 91 nm, being slightly smaller than those obtained in the wet state.