For enemy surveillance in outdoor environment, it is essential to distinguish whether the candidate target is a human or a four-footed animal. In this paper, we propose a method to distinguish the human from the four-footed animal using the ultra-wideband impulse radar system with 1 transmitter and 2 receivers (one on each side of the transmitter). The difference between the shortest and the longest path of the target refection is defined as target signature width. Since human is longer in vertical than in horizontal direction, the target signature widths at the receivers are both from the vertical direction and almost the same. However, the four-footed animal is long in horizontal and short in vertical direction. Depending on the directions of the animal facing to the antennas, the target signature widths could be much different at the receivers. Therefore, we propose a method to distinguish the human from the four-footed animal by using the ratio of the target signature widths at the receivers. The experimental results show that the proposed method can distinguish the human from the four-footed animal.