Mobius strips are three-dimensional geometrical structures, fascinating for their peculiar property of being surfaces with only one "side"-or, more technically, being "nonorientable" surfaces. Despite being easily realized artificially, the spontaneous emergence of these structures in nature is exceedingly rare. Here, we generate Mobius strips of optical polarization by tightly focusing the light beam emerging from a q-plate, a liquid crystal device that modifies the polarization of light in a space-variantmanner. Using a recently developed-method for the three-dimensional nanotomography of optical vector fields, we fully reconstruct the light polarization structure in the focal region, confirming the appearance of Mobius polarization structures. The preparation of such structured light modes may be important for complex light beam engineering and optical micro-and nanofabrication.