Voluntary control of respiration, especially via rhythmic nasal breathing, alleviates negative feelings such as fear and is used clinically to manage certain types of panic attacks. However, the neural substrates that link nasal breathing to fear circuits remains unknown. Here we show that during conditioned fear-induced freezing behavior, mice breathe at a steady rate (~4 Hz) which is strongly correlated with a predominant 4 Hz oscillation observed in the olfactory bulb and the prelimbic prefrontal cortex (plPFC), a structure critical for the expression of conditioned fear behaviors. We demonstrate anatomical and functional connectivity between the olfactory pathway and plPFC via circuit tracing and optogenetic approaches. Disrupting olfactory inputs significantly reduces the 4 Hz oscillation in the plPFC suggesting that respiration-related signals from the olfactory system play a role in entraining this fear-related signal. Surprisingly, we find that without olfactory inputs, freezing times are significantly prolonged. Collectively, our results indicate that olfactory inputs modulate rhythmic activity in fear circuits and suggest a neural pathway that may underlie the behavioral benefits of respiration-entrained olfactory signals.