An experimental study of beads formation during the electro spinning of nanofibers is reported. Electrostatic charging of a polymer solution (Poly Ethylene Oxide (PEO)) at the tip of a micro needle resulted in the formation of a Taylor cone, from the apex of which a single micro liquid jet is ejected. The jet was then electro spun and the resulting PEO nanofibers with average diameter of 300 nm were deposited on a grounded substrate. The collected nanofibers exhibited bead-like structures depending on: the polymer concentration in the electro spun solution, the applied voltage, the injection pressure and the needle-electrode distance. The beads formation has been a problem for almost a century and the current work approaches this problem form the fluid mechanics point of view. The micro jet near the nozzle exit was observed in-flight using digital holographic microscopy and the collected nanofibers were examined using Scanning Electron Microscopy (SEM). The initial fiber jet diameter, do, wave length of jet instability, λ, and the distance along the jet from the needle tip, x, are measured and reported. The results show a strong relationship between the initial jet instability (near the injector exit) and the bead formation on the collected nanofibers.