Large-conductance Ca²⁺-activated K⁺ channels (BK) regulate action potential (AP) properties and excitability in many central neurons. However, the properties and functional role of BK channels of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus (NA) have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at 7-9 days postnatal. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. Using excised patch single-channel recordings, we identified voltage-gated and Ca²⁺-dependent BK channels in PCMNs. The majority of BK channels exhibited persistent channel opening during voltage holding. These BK channels had a conductance of 237 pS. The channel dwell time increased exponentially as the membrane potential depolarized. Occasionally, some BK channels showed a transient channel opening or fast inactivation. Using whole-cell voltage clamp, we found that BK channel mediated outward currents had both transient and persistent components. Using whole-cell current clamp, we found that application of IBTX increased spike half-width in single APs and trains, and reduced the spike frequency-dependent AP broadening in trains. In addition, BK channel blockade suppressed fast afterhyperpolarization (fAHP) amplitude following APs. Furthermore, BK channel blockade significantly decreased spike frequency and spike frequency adaption (SFA). Collectively, these results demonstrate that PCMNs have BK channels which significantly regulate AP repolarization, fAHP, SFA and spike frequency. We conclude that activation of BK channels underlies one of the mechanisms for facilitation of PCMN excitability.