Recently, fibers and fabrics have been considered as promising platforms for low-cost flexible electronics and multifunctional fabrics, referred to as electronic fibers (e-fibers), electronic textiles (e-textiles), or smart textiles. Fiber- and fabric-shaped organic thin-film solar cells can be used over a wide range of applications as an energy harvester for smart textiles such as clothing, bags, curtains, tents, awnings, and shading elements. In the present study, to examine the optical absorption property of fiber- and fabric-shaped organic thin-film solar cells, we carried out geometrical optics simulations by using both the ray-tracing and transfer matrix methods for the resin-sealed photovoltaic fibers with core-sheath structure. It was found that the light absorption by single photovoltaic fiber with a appropriate thickness of sealing layer is approximately equivalent to that by the flat-panel solar cells. In addition, the light absorption by the photovoltaic fabrics composed of the sealed photovoltaic fibers was improved compared with the flat panel cells due to the interchange of light between fibers in the fabrics (increased by a maximum of 24 ％ for the plain-woven fabric). These results demonstrated that both the thickness controlling of transparent resin sealing layer and the weaving of photovoltaic fibers are a promising light management approach in fiber- and fabric-shaped organic thin-film solar cells.