Controlling wettability is of the key properties of solid surfaces from both fundamental and practical aspects. Wettability could be manipulated by tailoring surface topography and surface chemical compositions. The studies of natural phenomena resulted to the fact that for creating superhydrophobic surfaces both reduces in the surface energy and creating proper surface roughness are required. So far, a wide variety method have been used to induced surface roughness such as, anodic oxidation, plasma treatment, laser treatment, chemical vapor deposition, lithography, phase separation, electrospinning and sol-gel processing in combination with substances such as silanes and fluorochemicals. Electrospinning is a well-known method for manufacturing nanofibers while it is a straightforward method to produce fibers from polymer solutions, with diameters in the range of sub-micron and nanometer. It is revealed that nanofibers have the ability to create rough surfaces whereas there is no study on the effect of nanofibre diameter and created surface roughness in addition to its effect on surface hydrophobicity. Therefore in this research, fabricating superhydrophobic surface via tuning nanofibres diameter using electrospinning was investigated. For this purpose, polyacrylonitrile with different weights percentage was solved in N, N-dimethylformamide (DMF) and nanofibers with different diameters were produced. The samples characteristics was investigated by a variety methods including: determination of the nanofibers diameter, studying surface morphology with SEM microscopy, measurements of the contact angles, sliding angle, investigating surface roughness via AFM imaging and evaluation of the nanoweb pore size by image analysis. Investigation into the unfinished nanoweb hydrophobicity indicate that the hydrophilic nanoweb changed to a hydrophobic surface for the samples with diameter greater than 697 nm, coupled with contact angle of larger than 120?. Coating the nanofibers with the fluorocarbon enhances all samples hydrophobicity with a direct relation between diameter of the nanofibers and their repellent properties. So that superhydrophic surface was created by the fibers with the largest diameters by which water contact angle of 157? and sliding angle of about 3? was obtained. Also the comparison of the hydrophobicity of polyacrylonitrile nanofiber with its flat film shows that the results are consistent with Cassie- Baxter model. Keywords: Electrospinning, hydrobophicity, surface roughness, contact angle