An experimental investigation was conducted using an electrospray of polyetherimide (Ultem-1000 PEI) solutions in dichloroethane to produce fairly monodisperse, fine PEI particles. The effects of three key experimental parameters were investigatednamely, the applied voltage, the liquid flow rate, and the polymer concentration. The liquid flow rate has the most important effect in determining the particle size. An optimal range of flow rates often exists. Particles obtained within the optimal range have a narrower size distribution and a better morphology (dense and spherical), compared with those produced with other liquid flow rates. The ultimate goal of this research is to prepare carbon molecular sieve (CMS) particles by in-situ pyrolysis of the electrospray-generated PEI nanoparticles to be utilized in the preparation of membranes. Here, the CMS particles, which are prepared ex-situ via the pyrolysis of the electrospray PEI particles, are compared, in regard to their properties, with the CMS particles that were generated via the conventional grinding of pyrolyzed PEI pellets. They are determined to have generally similar structural properties.