Melt blowing is a technology for producing microfibrous nonwovens. The melt-blowing die is the key component of the melt-blowing device. In this study, a slot die and a swirl die were used to study the effects of die geometry on fiber motion and fiber attenuation in the melt-blowing process. The fiber paths in these two melt-blowing processes were recorded dynamically with a high-speed camera at a shutter speed of 3000 frames per second. The fiber path profiles, especially the whipping behavior, were for the first time obtained and presented. The recorded images were further processed to interpret the law of fiber motion and to determine the fiber velocity. A mathematical method was also constructed to qualify the fiber diameters instantly below the two dies, which are undetectable upon experimental measurement. The results show that fiber whipping in the slot-die melt-blowing process is a two-dimensional motion. In contrast, it appears as a spiral path in three dimensions in the swirl-die melt-blowing process. The swirl die creates more rapid fiber attenuation in the region near the die.