Melt blowing is a major process for producing nanofibrous nonwovens. Compared to studies on the air flow field and the fiber diameter measurement, much less has been done on the observations of whipping in the melt-blowing process. In this study, a high-speed camera was used to capture the fiber path below a single-orifice melt-blowing slot die. The behavior of loops resulted from whipping was revealed. The characteristics of the whipping amplitude, whipping frequency, and fiber velocity were obtained. Fiber attenuation contributed by whipping was calculated by measuring the perimeter of the loops. The study shows the laws of fiber whipping in a slot-die melt-blowing process and indicates that whipping plays a role in fiber attenuation.