A doublet of one-dimensional metallic bands on Au-stabilized Si(5 53) surface features different splitting due to the spin-orbit interaction. Density functional theory calculations reveal the origin of unequal magnitude of the splitting. Furthermore, different orientations of spin polarizations, almost perpendicular to each other, in both spin-orbit split bands are discovered. These observations are consistent with the Rashba effect and induced electric field in the system with out-of-plane and in-plane components. The results of calculations are confirmed by spin- and angle-resolved photoelectron spectroscopy measurements. The Si(5 53)-Au surface appears as a unique 1D Rashba system. (C) 2015 Elsevier B.V. All rights reserved.