Precise control of fiber diameter during electrospinning is very crucial for many applications. A systematic and quantitative study on the effects of processing variables enables us to control the properties of electrospun nanofibers. In this contribution, response surface methodology (RSM) was employed to quantitatively investigate the simultaneous effects of four of the most important parameters, namely solution concentration (C), spinning distance (d), applied voltage (V) and volume flow rate (Q), on mean fiber diameter (MFD) as well as standard deviation of fiber diameter (StdFD) in electrospinning of polyvinyl alcohol (PVA) nanofibers.