Mullite fibers with diameters from 400 nm to 10 mu m were fabricated from the sol-gel precursors using the electrospinning method. During the precursor synthesis, the hydrolysis was controlled to obtain highly viscous mullite sols. The viscous mullite sols were then diluted and mixed with a small amount of polyethylene oxide. Controlling the precursor rheology and spinning conditions, we obtained mullite fibers with the relatively uniform microstructure and narrow diameter distributions for each e-spinning condition. We carried out the mechanical tests for the electrospun mullite fibers since the mechanical performances of e-spin ceramic fibers have not been often reported. The tensile strengths of electrospun mullite fibers were determined using the single filament tensile test. The average tensile strength was 1.46 GPa for 5 mm gauge length, and 1.25 GPa for 10 mm gauge length. The Weibull modulus was estimated to be 3-4, which is comparable to commercial ceramic fibers. The fiber exhibited an average elastic modulus of 100 GPa. In this study, we show that controlling the hydrolysis can reduce the polymer additive amount required for electrospinning. Thus the electrospun mullite fiber has the similar mechanical properties to the dry spun counterparts.