The odors of predators used in animal models provide, in addition to electric footshock, an important means to investigate the neurobiology of fear. Studies indicate that cat odor and trimethylthiazoline (TMT), a synthetic compound isolated from fox feces, are often presented to rodents to induce fear-related responses including freezing, avoidance, stress hormone and, in some tests, risk assessment behavior. Furthermore, we report that different amounts of cat odor impregnated on small-, medium-, or large-sized cloths impact the display of fear-related behavior when presented to rats. That is, rats exposed to a large cat odor containing cloth exhibit an increase in fear behavior, particularly freezing, which remains at high levels in habituation tests administered over a period of 7 days. The large cloth also induces a long-lasting increase in avoidance behavior during repeated habituation and extinction tests. A review of the brain regions involved in predator odor-induced fear behavior indicates a modulatory role of the medial amygdala, bed nucleus of the stria terminalis, and dorsal premammillary nucleus. In addition, the basolateral amygdala is involved in fear behavior induced by cat odor but not TMT, and the central amygdala does not appear to play a major behavioral role in predator odor-induced fear. Future research involving the use of predator odor is likely to rapidly expand knowledge on the neurobiology of fear, which has implications for understanding fear-related psychopathology.