Various voltage-gated K+ currents were recently described in dorsal root ganglion (DRG) neurons. However, the characterization and diversity of voltage-gated K+ currents have not been well studied in trigeminal root ganglion (TRG) neurons, which are similar to the DRG neurons in terms of physiological roles and anatomy. This study was aimed to investigate the characteristics and diversity of voltage-gated K+ currents in acutely isolated TRG neurons of rat using whole cell patch clamp techniques. The first type (type I) had a rapid, transient outward current (IA) with the largest current size having a slow inactivation rate and a sustained delayed rectifier outward current (IK) that was small in size having a fast inactivation rate. The IA currents of this type were mostly blocked by TEA and 4-AP, K channel blockers whereas the IK current was inhibited by TEA but not by 4-AP. The second type had a large IA current with a slow inactivation rate and a medium size-sustained delayed IK current with a slow inactivation rate. In this second type (type II), the sensitivities of the IA or IK current by TEA and 4-AP were similar to those of the type I. The third type (type III) had a medium sized IA current with a fast inactivation rate and a large sustained IK current with the slow inactivation rate. In type III current, TEA decreased both IA and IK but 4-AP only blocked IA current. The fourth type (type IV) had a smallest IA with a fast inactivation rate and a large IK current with a slow inactivation rate. TEA or 4-AP similarly decreased the IA but the IK was only blocked by 4-AP. These findings suggest that at least four different voltage-gated K+ currents in biophysical and pharmacological properties exist in the TRG neurons of rats.