Melt or solution electrospinning are effective and direct techniques for producing nanoscale fibers. Polypropylene (PP) cannot be easily dissolved at ambient temperature. Thus, it is commonly electrospun in the melt state. However, compared with solution electrospun fibers, melt electrospun PP fibers are more uneven and with larger diameters. In this study, to remedy this problem, polar additives, namely stearic acid and sodium stearate, were added into pure PP. The effects of the additives were investigated. The results showed that in contrast to those of pure PP, the fiber diameter of PP with 8 wt. % stearic acid was decreased by 69.3 % (from 5.4 to 1.6 mu m). The smallest fiber diameter was 600 nm and the smallest average fiber diameter was 1.8 mu m when the sodium stearate contents were 10 and 8 wt. %, respectively. The addition of polar compounds altered not only the diameters of PP microfibers, but also the distribution of diameters, the processing current, and even the thermal properties of the fibers. The microcosmic mechanisms for these changes were interpreted.