Aim: Na+-activated K+ (Kna) channels set and stabilize resting membrane poten- tial in rat small dorsal root ganglion (DRG) neurons. However, whether Kna chan- nels play the same role in other size DRG neurons is still elusive. The aim of this study is to identify the existence and potential physiological functions of Kna channels in medium diameter (25-35 μm) DRG neurons. Methods: Inside-out and whole-cell patch-clamp were used to study the electrophysiological characteriza- tions of native Kna, channels. RT-PCR was used to identify the existence of Slack and Slick genes. Results: We report that Kna channels are required for depolariz- ing afterpotential (DAP) in medium sized rat DRG neurons. In inside-out patches, Ks, channels represented 201 pS unitary chord conductance and were activated by cytoplasmic Na+ [the half maximal effective concentration (EC50): 35 mmol/L] in 160 mmol/L symmetrical K+/K+ solution. Additionally, these Kna channels also represented cytoplasmic Cl--dependent activation. RT-PCR confirmed the exist- ence of Slack and Slick genes in DRG neurons. Tetrodotoxin (TTX, 100 nmol/L) completely blocked the DRG inward Na+ currents, and the following outward cur- rents which were thought to be Kna currents. The DAP was increased when extracellular Na+ was replaced by Li+. Conclusion: We conclude that Slack and Slick Kna channels are required for DAP of medium diameter rat DRG neurons that regulate DRG action potential repolarization.