Inspired by the self-cleaning silver ragwort leaf, we have recently fabricated a biomimetic super-hydrophobic fibrous mat surface comprising micro/nanoporous polystyrene (PS) microfibres via electrospinning. The rough surface of the silver ragwort leaf fibres, with nanometre-sized grooves along the fibre axis, was imitated by forming micro- and nanostructured pores on the electrospun fibre surface. The solvent composition ratios of tetrahydrofuran (THF) to N,N-dimethylformamide (DMF) in PS solutions were proved to be the key parameter to affect the fibre surface structures due to the various phase separation speeds of the solvents from PS fibres during electrospinning. The combination of the hierarchical surface roughness inherent in electrospun microfibrous PS mats and the low surface free energy of PS yielded a stable super-hydrophobicity with water contact angles as high as 159.5. for a 12 mg water droplet, exceeding that (147 degrees) of the silver ragwort leaf. Moreover, the hydrophobicity of the porous PS mat surface was found to increase on increasing the surface roughness of the microfibres.