Cylindrical micelles made of soluble and insoluble segments have found many interesting applications, for example, in templating the formation of inorganic nanocrystal arrays, controlled drug delivery, and bionanotechnology. Conventional methods for the preparation of cylindrical micelles are based on the judicious design of the molecular structures of the soluble and insoluble segments and the manipulation of the external parameters, such as the solvent, temperature, and guest ions/molecules. Here we report on the production of cylindrical micelles by extruding spherical micelles through nanoscale pores. The obtained cylindrical micelles and their transformation back into the spherical micelles are characterized using transmission electron microscopy imaging and dynamic laser light scattering. The extrusion process is continuous and simple and can be upgraded to large scales. We believe that our nanopore extrusion-based preparation method will provide enormous opportunities for the applications of block copolymer cylindrical micelles in nanotechnology and medicine.