Electrospinning is a method that produces fibers with diameters ranging from a few micrometers down to under hundred nanometers. In this study, the influence of temperature and relative humidity on the morphology of electrospun polyetherimide (PEI) fibers is investigated. 1-methyl-2-pyrrolidinone (NMP) is used as a solvent. Surface morphologies and diameters of electrospun PEI fibers are examined by Field-Emission Scanning Electron Microscopy (FESEM). The experimental results show that average diameter of electrospun PEI fibers increases with increasing relative humidity at all ambient temperatures. As the temperature increase, average diameter of electrospun PEI fibers decreases. Surface roughness of the fibers increases with increasing of RH. The whole of the electrospun PEI fibers obtained are circular shaped.