Compared to unmodified carbons and even some metal materials, nitrogen-doped carbons have been found to exhibit better performance for reducing oxygen-oxygen bonds, a key step in electroreduction of both O2 (an important reaction in energy applications) and H2O2 (an important reaction in sensing and biosensing). Previous studies from our lab revealed that thermal decomposition of urea in the presence of carbon fiber (CF) results in N-doped that exhibited good electrocatalytic properties for H2O2 reduction. However, previous methods of sealing ultramicroelectrodes (UMEs) made from N-doped CF using laser heating of borosilicate capillaries and epoxy seemed to affect surface nitrogen contents and electrocatalytic properties. In this work, we evaluate paraffin sealing as a strategy for preparing UMEs in a way that minimizes effects on important surface nitrogen species so that electrocatalytic properties of the N-doped CF towards H2O2 reduction can be retained.