The mechanical buckling of one-dimensional Si nanoribbons with a thickness contrast was investigated. For Si stripes with a small thickness difference, each section was found to undergo its own buckling with characteristic wavelengths and wave amplitudes, depending on their thicknesses. On the other hand, unusual buckling occurred for Si ribbons with large thickness differences. For this case, the thinned sections were uniformly buckled, and absorbed a large portion of externally applied strain. On the contrary, the thicker parts of the ribbon were buckled nonuniformly, i.e. buckling occurred in central regions only, with an almost flat configuration at both ends of the thicker parts. Buckling mechanics can qualitatively explain the observed buckling of the Si ribbons with a small thickness contrast, while the finite length effect should be considered for the case of the Si ribbons with a large thickness contrast. Considering the fact that real functional devices are not uniform in thickness, the present work helps to understand the complex buckling behavior of mechanical systems with a wide range of thickness contrasts. (C) 2017 Elsevier B.V. All rights reserved.