The pore space structure of MGA-95 and ESPA membranes has been investigated by the smallangle X-ray scattering (SAXS). The pore radii as the parameters forming the skeleton of the pore space of the reverse-osmosis composite membranes have been established. Three types of scattering pores (sphere, disc, and cylinder) are found in the region of the X-ray scattering vector of 0.171 < s < 0.538 nm(-1), and their average radii of gyration have been determined. The pore structure of the MGA-95 and ESPA membranes, which can be described in terms of the self-affine fractal concept, has been revealed. In the region of the scattering vector of 0.245 < s < 0.342 nm(-1) (the average pores with 9.2 < r < 12.8 nm) the pore structure corresponds to the "stacked sphere" model with the long straight channels with D = 1.2 and D = 1.3 fractal indices. The pores with r similar to 20 nm form the sinuous channels with the fractal indices of D = 2.1 and 2.8, respectively. Scattering at 0.391 < s < 0.538 nm(-1) (5.8 < r < 8.0 nm) occurs on compact monopores with the smooth surface and a fractal index of D = 3.9 (D = 4, Porod regime).