Mesoporous materials are of great interest in fields of catalysis, biosensing, gas sensing and adsorption due to their high specific surface area as compared to macroporous materials and lower pore diffusion resistance when compared to microporous materials. The microphase separation property of block copolymers can be used to obtain mesoporous materials by selectively etching one of its polymer blocks. In this study, we have successfully demonstrated the synthesis of mesoporous poly (styrene-block-methylmethacrylate) (PS-b-PMMA) nanofibers using electrospinning. Morphology of these PS-b-PMMA fibers obtained by electrospinning depends on a number of process as well as solution parameters which were tuned to obtain long uniform and continuous fibers as confirmed by field emission electron microscopy. The nanofibers thus obtained were thermally annealed to assist the phase separation. Later the fibers were exposed to ultraviolet radiation followed by etching with a weak acid to remove the degraded polymer block leading to mesoporous PS-b-PMMA nanofibers, as confirmed by transmission electron microscopy. We also demonstrate the direct synthesis of porous PS-b-PMMA fibers driven by the rapid vaporization of the highly volatile solvent. A comprehensive study of the effect of electrospinning solvent and annealing and etching conditions on the specific surface area, porous structure including pore volume and pore size distribution is carried out using the nitrogen adsorption-desorption isotherms and the small angle X-ray scattering (SAXS). We also analyzed the mesoporous nature of PS-b-PMMA nanofibers using fractal dimension analysis. © 2018 Elsevier B.V.