Spin-echo small-angle neutron scattering (SESANS) is used to study the magnetic domain structure of an Ni layer electrodeposited onto a Cu substrate. The domain structure of the sample corresponds to the hard-plane model, where the magnetization in the domains is directed perpendicular to the layer; the domain length coincides with the thickness of the layer of the order of 10 μm and its width is of the order of 1 μm. The pair correlation function of the magnetization has been directly measured. It is established that the width of the domain depends linearly on its thickness. The domain structure does not depend on heating at temperatures below T_C of nickel. Annealing at T > T_C results in a reconstruction of the domain structure with a tendency to the easy-plane model, i.e. with domain magnetization in the plane. The multiple scattering effect is studied and may be taken into account. This experiment demonstrates the possibilities of magnetic SESANS. Some aspects of this novel technique are pointed out.