Autonomic nerves convey essential neural signals that regulate vital body functions. Recording clearly distinctive physiological neural signals from autonomic nerves will help develop new treatments for restoring regulatory functions. However, this is very challenging due to the small nature of autonomic nerves and the low-amplitude signals from their small axons. We developed a multi-channel, high-density, intraneural carbon fiber microelectrode array (CFMA) with ultra-small electrodes (8-9 µm in diameter, 150-250 µm in length) for recording physiological action potentials from small autonomic nerves. In this study, we inserted CFMA with up to 16 recording carbon fibers in the cervical vagus nerve of 22 isoflurane-anesthetized rats. We recorded action potentials with peak-to-peak amplitudes of 15.1-91.7 µV and signal-to-noise ratios of 2.0-8.3 on multiple carbon fibers per experiment, determined conduction velocities of some vagal signals in the afferent (0.7-4.4 m/s) and efferent (0.7-8.8 m/s) directions, and monitored firing rate changes in breathing and blood glucose modulated conditions. Overall, these experiments demonstrated that CFMA is a novel interface for in-vivo intraneural action potential recordings. This work is considerable progress towards the comprehensive understanding of physiological neural signaling in vital regulatory functions controlled by autonomic nerves.